Publications

Hydroxyl radical (OH) is a key oxidant that triggers atmospheric oxidation chemistry in both gas and aqueous phases. The current understanding of its aqueous sources is mainly based on known bulk (photo)chemical processes, uptake from gaseous OH, or related to interfacial O 3 and NO 3 radical-driven chemistry. Here, we present experimental evidence that OH radicals are spontaneously produced at the air–water interface of aqueous droplets in the dark and the absence of known precursors, possibly due to the strong electric field that forms at such interfaces. The measured OH production rates in atmospherically relevant droplets are comparable to or significantly higher than those from known aqueous bulk sources, especially in the dark. As aqueous droplets are ubiquitous in the troposphere, this interfacial source of OH radicals should significantly impact atmospheric multiphase oxidation chemistry, with substantial implications on air quality, climate, and health.

Events of high dust loading are extreme meteorological phenomena with important climate and health implications. Therefore, early forecasting is critical for mitigating their adverse effects. Dust modeling is a long-standing challenge due to the multiscale nature of the governing meteorological dynamics and the complex coupling between atmospheric particles and the underlying atmospheric flow patterns. While physics-based numerical modeling is commonly being used, we propose a meteorological-based deep multi-task learning approach for forecasting dust events. Our approach consists of forecasting the local PM10 (primary task) measured in situ, and simultaneously to predict the satellite-based regional PM10 (auxiliary task); thus, leveraging valuable information from a correlated task. We use 18 years of regional meteorological data to train a neural forecast model for dust events in Israel. Twenty-four hours before the dust event, the model can detect 76% of the events with even higher predictability of winter and spring events. Further analysis shows that local dynamics drive most misclassified events, meaning that the coherent driving meteorology in the region holds a predictive skill. Further, we use machine-learning interpretability methods to reveal the meteorological patterns the model has learned, thus highlighting the important features that govern dust events in the Middle East, being primarily lower-tropospheric winds, and Aerosol Optical Depth.

Soot particles (SP) are ubiquitous components of atmospheric particulate matter and have been shown to cause various adverse health effects. In the atmosphere, freshly emitted SP can be coated by condensed low-volatility secondary organic and inorganic species. In addition, gas-phase oxidants may react with the surface of SP. Due to the chemical and physical resemblance of SP carbon backbone with polyaromatic hydrocarbon species and their potent oxidation products, we investigated the biological responses of BEAS-2B lung epithelial cells following exposure to fresh- and photochemically aged-SP at the air-liquid interface. A comprehensive physical and chemical aerosol characterization was performed to depict the atmospheric transformations of SP, showing that photochemical aging increased the organic carbon fraction and the oxidation state of the SP. RNA-sequencing and qPCR analysis showed varying gene expression profiles for fresh- and aged-SP. Exposure to aged-SP increased DNA damage, oxidative damage, and upregulation of NRF2-mediated oxidative stress response genes compared to fresh-SP. Furthermore, aged-SP augmented inflammatory cytokine secretion and activated AhR-response, as evidenced by increased expression of AhR-responsive genes. These results indicate that oxidative stress, inflammation, and DNA damage play a key role in the cytotoxicity of SP in BEAS-2B cells, where aging leads to higher toxic responses. Collectively, our results suggest that photochemical aging may increase SP toxicity through surface modifications that lead to an increased toxic response by activating different molecular pathways.

Human health is linked to climatic factors in complex ways, and climate change can have profound direct and indirect impacts on the health status of any given region. Susceptibility to climate change is modulated by biological, ecological and socio-political factors such as age, gender, geographic location, socio-economic status, occupation, health status and housing conditions, among other. In the Eastern Mediterranean and Middle East (EMME), climatic factors known to affect human health include extreme heat, water shortages and air pollution. Furthermore, the epidemiology of vector-borne diseases (VBDs) and the health consequences of population displacement are also influenced by climate change in this region. To inform future policies for adaptation and mitigation measures, and based on an extensive review of the available knowledge, we recommend several research priorities for the region. These include the generation of more empirical evidence on exposure-response functions involving climate change and specific health outcomes, the development of appropriate methodologies to evaluate the physical and psychological effects of climate change on vulnerable populations, determining how climate change alters the ecological determinants of human health, improving our understanding of the effects of long-term exposure to heat stress and air pollution, and evaluating the interactions between adaptation and mitigation strategies. Because national boundaries do not limit most climate-related factors expected to impact human health, we propose that adaptation/mitigation policies must have a regional scope, and therefore require collaborative efforts among EMME nations. Policy suggestions include a decisive region-wide decarbonisation, the integration of environmentally driven morbidity and mortality data throughout the region, advancing the development and widespread use of affordable technologies for the production and management of drinking water by non-traditional means, the development of comprehensive strategies to improve the health status of displaced populations, and fostering regional networks for monitoring and controlling the spread of infectious diseases and disease vectors.

We describe the design and performance of a lightweight broadband cavity-enhanced spectrometer for measurement of NO2 on uncrewed aerial vehicles and light aircraft. The instrument uses a light-emitting diode (LED) centered at 457 nm, high-finesse mirrors (reflectivity = 0.999963 at 450 nm), and a grating spectrometer to determine optical extinction coefficients between 430 and 476 nm, which are fit with custom spectral fitting software and published absorption cross sections. The instrument weighs 3.05 kg and has a power consumption of less than 35 W at 25 ?C. A ground calibration unit provides helium and zero air flows to periodically determine the reflectivity of the cavity mirrors using known Rayleigh scattering cross sections. The precision (1 sigma) for laboratory measurements is 43 ppt NO2 in 1 s and 7 ppt NO2 in 30 s. Measurement of air with known NO2 mixing ratios in the range of 0- 70 ppb agreed with the known values within 0.3 % (slope = 0.997 +/- 0.007; r2 = 0.99983). We demonstrate instrument performance using vertical profiles of the NO2 mixing ratio acquired on board an uncrewed aerial vehicle between 0 and 110 m above ground level in Boulder, Colorado.

The microbiome of atmospheric dust events has raised increasing interest in the last decade, resulting in numerous studies that characterized the different parameters affecting the composition of the atmospheric microbiome, that is, the aerobiome. However, less is known about the functional profile of the aerobiome and how it compares with other environments. Here, we describe the results of shotgun metagenome analysis conducted on a representative set of particulate matter (PM) samples taken in Israel under dusty and nondusty conditions. We compared the functional profiles of these samples to local metagenomes collected from soils, sea, and leaf surfaces and to PM collected in Saudi Arabia, in order to link between the sampled aerosols and potential sources that contribute to the aerobiome. We found that PM samples collected in Israel most resembled Saudi Arabian dust and Israeli soils in both community composition and functional genes profile. In addition, we found significant differences in the abundances of genes associated with anthropogenic activity. Specifically, the examined dust exhibited a significantly higher abundance of genes associated with the biodegradation of organic contaminants, mostly benzoate and aminobenzoate, compared with all other examined environments. These preliminary results suggest that an anthropogenic impact on the aerobiome composition and functional profile is widespread, and pave the path to understanding the role of dust storms in disseminating microorganisms in various environments, spreading various traits, and affecting humans, livestock, plants, and ecosystem health.

Straw burning comprises more than 30% of all types of burned biomass in Asia, while the estimation of the emitted aerosols' direct radiative forcing effect suffers from large uncertainties, especially when atmospheric aging processes are considered. In this study, the light absorption properties of primary and aged straw burning aerosols in open fire were characterized at 7 wavelengths ranging from 370 nm to 950 nm in a chamber. The primary rice, corn and wheat straw burning bulk aerosols together had a mass absorption efficiency (MAE) of 2.43 ± 1.36 m2 g−1 at 520 nm and an absorption Ångström exponent (AAE) of 1.93 ± 0.71, while the primary sorghum straw burning bulk aerosols were characterized by a relatively lower MAE of 0.95 ± 0.54 m2 g−1 and a higher AAE of 4.80 ± 0.68. Both the MAE and AAE of primary aerosols can be well parameterized by the (PM-BC)/BC ratio (in wt.). The MAE of black carbon (BC) increased by 11–190% during photoreactions equivalent to 16–60 h of atmospheric aging, which was positively correlated with the (PM-BC)/(BC) ratio. The MAE of organic aerosols first slightly increased or leveled off, and then decreased. Specifically, at 370 nm, the first growth/plateau stage lasted until OH exposure reached 0.47–1.29 × 1011 molecule cm−3 s, and the following period exhibited decay rates of 1.0–2.8 × 10−12 cm3 molecule−1 s−1 against the OH radical, corresponding to half-lives of 46–134 h in a typical ambient condition. During photoreactions, competition among the lensing effect, growth/bleach of organic chromophores, and particle mass and size growth complicated the evolution of the direct radiative forcing effect. It is concluded that rice and corn straw burning aerosols maintained a warming effect after aging, while the cooling effect of fresh sorghum straw burning aerosols increased with aging.

Bacterial ice nucleation proteins (INPs) can cause frost damage to plants by nucleating ice formation at high sub-zero temperatures. Modeling of Pseudomonas borealis INP by AlphaFold suggests that the central domain of 65 tandem sixteen-residue repeats forms a beta-solenoid with arrays of outward-pointing threonines and tyrosines, which may organize water molecules into an ice-like pattern. Here we report that mutating some of these residues in a central segment of P. borealis INP, expressed in Escherichia coli, decreases ice nucleation activity more than the section’s deletion. Insertion of a bulky domain has the same effect, indicating that the continuity of the water-organizing repeats is critical for optimal activity. The ~10 C-terminal coils differ from the other 55 coils in being more basic and lacking water-organizing motifs; deletion of this region eliminates INP activity. We show through sequence modifications how arrays of conserved motifs form the large ice-nucleating surface required for potency.

Humic-like substances (HULIS) account for a major redox-active fraction of biomass burning organic aerosols (BBOA). During atmospheric transport, fresh acidic BB-HULIS in droplets and humid aerosols are subject to neutralization and pH-modified aging process. In this study, solutions containing HULIS isolated from wood smoldering emissions were first adjusted with NaOH and NH3 to pH values in the range of 3.6–9.0 and then aged under oxic dark conditions. Evolution of HULIS oxidative potential (OP) and total peroxide content (equivalent H2O2 concentration, H2O2eq) were measured together with the changes in solution absorbance and chemical composition. Notable immediate responses such as peroxide generation, HULIS autoxidation, and an increase in OP and light absorption were observed under alkaline conditions. Initial H2O2eq, OP, and absorption increased exponentially with pH, regardless of the alkaline species added. Dark aging further oxidized the HULIS and led to pH-dependent toxic and chemical changes, exhibiting an alkaline-facilitated initial increase followed by a decrease of OP and H2O2eq. Although highly correlated with HULIS OP, the contributions of H2O2eq to OP are minor but increased both with solution pH and dark aging time. Alkalinity-assisted autoxidation of phenolic compounds and quinoids with concomitant formation of H2O2 and other alkalinity-favored peroxide oxidation reactions are proposed here for explaining the observed HULIS OP and chemical changes in the dark. Our findings suggest that alkaline neutralization of fresh BB-HULIS represents a previously overlooked peroxide source and pathway for modifying aerosol redox-activity and composition. Additionally, these findings imply that the lung fluid neutral environment can modify the OP and peroxide content of inhaled BB-HULIS. The results also suggest that common separation protocols of HULIS using base extraction methods should be treated with caution when evaluating and comparing their composition, absorption, and relative toxicity.

Atmospheric particles were sampled in Rehovot, Israel during a national Lag Ba'Omer bonfire festival as a case study to investigate the physical and chemical transformations of mixed mineral dust and biomass burning (BB) aerosols. Aerosol mass spectrometry was used in situ to characterize aging and chemical evolution of BB aerosols in real time throughout the event. During this dynamic period of BB emissions, particle samples were collected for chemical imaging using spectromicroscopy techniques. Computer-controlled scanning electron microscopy with energy dispersive X-ray analysis identified multiple particle types including highly carbonaceous (54–83%) particles, aged mineral dust (1–6%), and sulfur-containing particles (17–41%). Synchrotron-based scanning transmission X-ray microscopy coupled with near edge X-ray absorption fine structure (STXM/NEXAFS) was used to assess the internal chemical heterogeneity of individual BB particles and the morphology of soot inclusions. The observed higher contribution of mixed component particles along with an increase in particle organic volume fraction suggests an atmospheric aging process, consistent with in situ measurements. An estimation method for particle component masses (i.e., organics, elemental carbon, and inorganics) inferred from STXM measurements was used to determine quantitative mixing state metrics of particles based on entropy-derived diversity measures for different periods of the BB event. In general, there was a small difference in the particle-specific diversity among the samples (Dα = 1.3–1.8). However, the disparity from the bulk population diversity observed during the intense periods was found to have high values of Dγ = 2.5–2.9, while particles collected outside of the burning event displayed lower bulk diversity of Dγ = 1.5–2.0. Quantitative methods obtained from chemical imaging measurements presented here will serve to accurately characterize the evolution of mixed BB aerosols within urban environments.

Delivering medication to the lungs via nebulization of pharmaceuticals is a noninvasive and efficient therapy route, particularly for respiratory diseases. The recent worldwide severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) pandemic urges the development of such therapies as an effective alternative to vaccines. The main difficulties in using inhalation therapy are the development of effective medicine and methods to stabilize the biological molecules and transfer them to the lungs efficiently following nebulization. We have developed a high-affinity angiotensin-converting enzyme 2 (ACE2) receptor-binding domain (RBD-62) that can be used as a medication to inhibit infection with SARS-CoV-2 and its variants. In this study, we established a nebulization protocol for drug delivery by inhalation using two commercial vibrating mesh (VM) nebulizers (Aerogen Solo and PARI eFlow) that generate similar mist size distribution in a size range that allows efficient deposition in the small respiratory airway. In a series of experiments, we show the high activity of RBD-62, interferon-α2 (IFN-α2), and other proteins following nebulization. The addition of gelatin significantly stabilizes the proteins and enhances the fractions of active proteins after nebulization, minimizing the medication dosage. Furthermore, hamster inhalation experiments verified the feasibility of the protocol in pulmonary drug delivery. In short, the gelatin-modified RBD-62 formulation in coordination with VM nebulizer can be used as a therapy to cure SARS-CoV-2.

The atmospheric aging of volatile organic compounds leads to the formation of complex mixtures of highly oxidized secondary organic aerosols (SOAs). State-of-the-art mass spectrometry (MS) has become a pivotal tool for their chemical characterization. In this study, we characterized the chemical complexity of naphthalene-derived SOA by three different time-of-flight (TOF) mass spectrometric techniques applying electron ionization: high-resolution–TOF–aerosol MS (AMS), direct inlet probe (DIP)–high-resolution TOFMS, and thermal desorptioncomprehensive two-dimensional gas chromatographyTOFMS (GC × GC). We discuss AMS as an online, DIP as an atline, and GC × GC as an offline technique to compare their informative value for studying the oxidation state, volatility, and molecular composition of laboratory-generated SOA. For GC × GC, the accessible organic content was limited to (semi-)­volatile compounds and supported a reliable assignment of the molecular composition. DIP and AMS were used to derive secondary parameters such as O/C and H/C ratios, the general functionality of the compound classes and their abundance upon photochemical aging. Thereby, while the induced pyrolysis in the AMS extended the accessibility range to polar, high-molecular-weight compounds, thermal fragmentation also led to limited molecular information. For DIP, low-volatility compounds could be volatilized and the high mass resolution was useful to resolve isobaric mass fragments and assign reliable sum formulas of fragments and molecular ions. Although no single technique can provide information to describe the full chemical complexity of the SOA, AMS, DIP, and GC × GC in their complementarity are well suited to investigate the impact of SOA on health and environment.

Secondary organic aerosols (SOAs) affect incoming solar radiation by interacting with light at ultraviolet and visible wavelength ranges. However, the relationship between the chemical composition and optical properties of SOA is still not well understood. In this study, the complex refractive index (RI) of SOA produced from OH oxidation of naphthalene in the presence of nitrogen oxides (NOx) was retrieved online in the wavelength range of 315–650 nm and the bulk chemical composition of the SOA was characterized by an online high-resolution time-of-flight mass spectrometer. In addition, the molecular-level composition of brown carbon chromophores was determined using high-performance liquid chromatography coupled to a photodiode array detector and a high-resolution mass spectrometer. The real part of the RI of the SOA increases with both the NOx/naphthalene ratio and aging time, likely due to the increased mean polarizability and decreased molecular weight due to fragmentation. Highly absorbing nitroaromatics (e.g., C6H5NO4, C7H7NO4, C7H5NO5, C8H5NO5) produced under higher NOx conditions contribute significantly to the light absorption of the SOA. The imaginary part of the RI linearly increases with the NOx/VOCs ratio due to the formation of nitroaromatic compounds. As a function of aging, the imaginary RI increases with the O/C ratio (slope = 0.024), mainly attributed to the achieved higher NOx/VOCs ratio, which favors the formation of light-absorbing nitroaromatics. The light-absorbing enhancement is not as significant with extensive aging as it is under a lower aging time due to the opening of aromatic rings by reactions.

We investigate the chemical composition of organic light-absorbing components, also known as brown carbon (BrC) chromophores, formed in a proxy of anthropogenic secondary organic aerosol generated from the photooxidation of naphthalene (naph-SOA) in the absence and presence of NOx. High-performance liquid chromatography equipped with a photodiode array detector and electrospray ionization high-resolution mass spectrometer is employed to characterize naph-SOA and its BrC components. We provide molecular-level insights into the chemical composition and optical properties of individual naph-SOA components and investigate their BrC relevance. This work reveals the formation of strongly absorbing nitro-aromatic chromophores under high-NOx conditions and describes their degradation during atmospheric aging. NOx addition enhanced the light absorption of naph-SOA while reducing wavelength-dependence, as seen by the mass absorption coefficient (MAC) and absorption Ångström exponent (AAE). Optical parameters of naph-SOA generated under low- and high-NOx conditions showed a range of values from MACOM 405nm ∼ 0.12 m2 g–1 and AAE300–450nm ∼ 8.87 (low-NOx) to MACOM 405nm ∼ 0.19 m2 g–1 and AAE300–450nm ∼ 7.59 (high-NOx), consistent with “very weak” and “weak” BrC optical classes, respectively. The weak-BrC class is commonly attributed to biomass smoldering emissions, which appear to have optical properties comparable with the naph-SOA. Molecular chromophores contributing to naphthalene BrC absorption were identified with substantial nitro-aromatics, indicating that these species may be used as source-specific markers of BrC related to the anthropogenic emissions.

The atmosphere plays an important role in transporting microorganisms on a global scale, yet the processes affecting the composition of the airborne microbiome, the aerobiome, are not fully outlined. Here we present the community compositions of bacteria and fungi obtained by DNA amplicon-sequencing of aerosol samples collected in a size-resolved manner during nine consecutive days in central Israel. The campaign captured dust events originating from the Sahara and the Arabian deserts, as well as days without dust (“clear days”). We found that the source of the aerosol was the main variable contributing to the composition of both fungal and bacterial communities. Significant differences were also observed between communities representing particles of different sizes. We show evidence for the significant transport of bacteria as cell-aggregates and/or via bacterial attachment to particles during dust events. Our findings further point to the mixing of local and transported bacterial communities, observed mostly in particles smaller than 0.6 μm in diameter, representing bacterial single cells. Fungal communities showed the highest dependence on the source of the aerosols, along with significant daily variability, and without significant mixing between sources, possibly due to their larger aerodynamic size and shorter atmospheric residence times. These results, obtained under highly varied atmospheric conditions, provide significant assurances to previously raised hypotheses and could set the course for future studies on aerobiome composition.

Airborne microbial communities directly impact the health of humans, animals, plants, and receiving ecosystems. While airborne bacterial and fungal communities have been studied by both cultivation-based methods and metabarcoding surveys targeting specific molecular markers, fewer studies have used shotgun metagenomics to study the airborne mycobiome. We analyzed the diversity and relative abundance of fungi in nine airborne metagenomes collected on clear days ( "background ") and during dust storms in the Eastern Mediterranean. The negative correlation between the relative abundance of fungal reads and the concentrations of atmospheric particulate matter having an aerodynamic diameter smaller than 10 mu m (PM10) indicate that dust storms lower the proportion of fungi in the airborne microbiome, possibly due to the lower relative abundance of fungi in the dust storm source regions and/or more effective transport of bacteria by the dust. Airborne fungal community composition was altered by the dust storms, particularly those originated from Syria, which was enriched with xerophilic fungi. We reconstructed a high-quality fungal metagenome-assembled genome (MAG) from the order Cladosporiales, which include fungi known to adapt to environmental extremes commonly faced by airborne microbes. The negative correlation between the relative abundance of Cladosporiales MAG and PM10 concentrations indicate that its origin is dominated by local sources and likely includes the indoor environments found in the city.

Sea spray aerosol (SSA) formation have a major role in the climate system, but measurements at a global-scale of this micro-scale process are highly challenging. We measured high-resolution temporal patterns of SSA number concentration over the Atlantic Ocean, Caribbean Sea, and the Pacific Ocean covering over 42,000 km. We discovered a ubiquitous 24-hour rhythm to the SSA number concentration, with concentrations increasing after sunrise, remaining higher during the day, and returning to predawn values after sunset. The presence of dominating continental aerosol transport can mask the SSA cycle. We did not find significant links between the diel cycle of SSA number concentration and diel variations of surface winds, atmospheric physical properties, radiation, pollution, nor oceanic physical properties. However, the daily mean sea surface temperature positively correlated with the magnitude of the day-to-nighttime increase in SSA concentration. Parallel diel patterns in particle sizes were also detected in near-surface waters attributed to variations in the size of particles smaller than ~1 µm. These variations may point to microbial day-tonight modulation of bubble-bursting dynamics as a possible cause of the SSA cycle.

Personal exposure PM samples aid in determining the sources and chemical composition of real-world exposures, particularly in settings with household air pollution. However, their use in toxicological research is limited, despite uncertainty regarding health effects in these settings and evidence of differential toxicity among PM2.5 sources and components. This study used women's PM2.5 exposure samples collected using personal exposure monitoring in rural villages in three Chinese provinces (Beijing, Shanxi, and Sichuan) during summer and winter. Water-soluble organic carbon, ions, elements, and organic tracers (e.g. levoglucosan and polycyclic aromatic hydrocarbons [PAHs]) were quantified in water and organic PM2.5 extracts. Human lung epithelial cells (A549) were exposed to the extracts. Cell death, reactive oxygen species (ROS), and gene expression were measured. Biomass burning contributions were higher in Sichuan samples than in Beijing or Shanxi. Some PM characteristics (total PAHs and coal combustion source contributions) and biological effects of organic extract exposures (cell death, ROS, and cytokine gene expression) shared a common trend of higher levels and effects in winter than in summer for Shanxi and Beijing but no seasonal differences in Sichuan. Modulation of phase I/AhR-related genes (cyp1a1 and cyp1b1) and phase II/oxidative stress-related genes (HO-1, SOD1/2, NQO-1, and catalase) was either low or insignificant, without clear trends between samples. No significant cell death or ROS production was observed for water extract treatments among all sites and seasons, even at possible higher concentrations tested. These results support organic components, particularly PAHs, as essential drivers of biological effects, which is consistent with some other evidence from ambient PM2.5.

Portable aethalometers are commonly used for online measurements of light-absorbing carbonaceous particles (LAC). However, they require strict calibration. In this study, the performance of a micro-aethalometer (MA200 with polytetrafluoroethylene filter) in charactering brown carbon aerosol (BrC) absorption was evaluated in comparison with reference materials and techniques that included bulk solution absorbance and Mie-theory based particle extinction retrieval via broadband cavity enhanced spectrometer (BBCES). Continuous-wavelength resolved (300–650 nm) imaginary refractive index (kBrC) was derived with these methods for various BrC proxies and standard materials representing a wide range of sources and absorbing abilities, including the strongly absorbing nigrosin, pahokee peat fluvic acid (PPFA), tar aerosol from wood pyrolysis, humic-like substance (HULIS) separated from wood smoldering burning emissions, and secondary organic aerosols (SOA) from photochemical oxidation of indole and naphthalene in the presence of NOx. The BrC and nigrosin optical results by bulk solution absorption are comparable with the properties retrieved from BBCES. The MA200 raw measurements provide reliable absorption Ångström exponent (AAE) but overestimate kBrC largely. The parameterized overestimates against reference methods depend on light absorption strength, so that the MA200 overestimates more for the less absorbing BrC. The correction factor for MA200 can be expressed well as an exponential function of kBrC or particle single scattering albedo (SSA), and also as a power-law function of the MA200 raw results derived BrC mass absorption efficiency (MAE). The ensemble correction factor regressed for all these BrC and nigrosin is 2.8 based on bulk absorption and 2.7 using BBCES result as reference. Simple radiative forcing (SRF) calculations for different scenarios using the correction for MA200, show consistent SRF when using the aethalometer results after the kBrC-dependent correction.

The composition of organic aerosol has a pivotal influence on aerosol properties such as toxicity and cloud droplet formation capability, which could affect both climate and air quality. However, a comprehensive and fundamental understanding of the chemical and physical processes that occur in nanometer-sized atmospheric particles remains a challenge that severely limits the quantification and predictive capabilities of aerosol formation pathways. Here, we investigated the effects of a fundamental and hitherto unconsidered physical property of nanoparticlesthe Laplace pressure. By studying the reaction of glyoxal with ammonium sulfate, both ubiquitous and important atmospheric constituents, we show that high pressure can significantly affect the chemical processes that occur in atmospheric ultrafine particles (i.e., particles

Asian dust is an important source of atmospheric ice-nucleating particles (INPs). However, the freezing activity of airborne Asian dust, especially its sensitivity to particle size, is poorly understood. In this study we report the first INP measurement of size-resolved airborne mineral dust collected during East Asian dust events. The measured total INP concentrations in the immersion mode ranged from 10(-2) to 10(2) L-1 in dust events at temperatures between 25 and 5 degrees C. The average contributions of heat-sensitive INPs at three temperatures, -10, 15, and 20 degrees C, were 81 +/- 12 %, 70 +/- 15 %, and 38 +/- 21 %, respectively, suggesting that proteinaceous biological materials have a substantial effect on the ice nucleation properties of Asian airborne mineral dust at high temperatures. The dust particles which originated from China's northwest deserts are more efficient INPs compared to those from northern regions. In general, there was no significant difference in the ice nucleation properties between East Asian dust particles and other regions in the world. An explicit size dependence of both INP concentration and surface ice-active-site density was observed. The nucleation efficiency of dust particles increased with increasing particle size, while the INP concentration first increased rapidly and then leveled, due to the significant decrease in the number concentration of larger particles. A new set of parameterizations for INP activity based on size-resolved nucleation properties of Asian mineral dust particles were developed over an extended temperature range (35 to 6 degrees C). These size-dependent parameterizations require only particle size distribution as input and can be easily applied in models.

This study provides molecular insights into the light absorption properties of biomass burning (BB) brown carbon (BrC) through the chemical characterization of tar condensates generated from heated wood pellets at oxidative and pyrolysis conditions. Both liquid tar condensates separated into "darker oily"and "lighter aqueous"immiscible phases. The molecular composition of these samples was investigated using reversed-phase liquid chromatography coupled with a photodiode array detector and a high-resolution mass spectrometer. The results revealed two sets of BrC chromophores: (1) common to all four samples and (2) specific to the "oily"fractions. The common BrC chromophores consist of polar, monoaromatic species. The oil-specific BrC chromophores include less-polar and nonpolar polyaromatic compounds. The most-light-absorbing pyrolysis oily phase (PO) was aerosolized and size-separated using a cascade impactor to compare the composition and optical properties of the bulk versus the aerosolized BrC. The mass absorption coefficient (MAC300-500 nm) of aerosolized PO increased compared to that of the bulk, due to gas-phase partitioning of more volatile and less absorbing chromophores. The optical properties of the aerosolized PO were consistent with previously reported ambient BB BrC measurements. These results suggest the darkening of atmospheric BrC following non-reactive evaporation that transforms the optical properties and composition of aged BrC aerosols.

Globally consistent measurements of airborne metal concentrations in fine particulate matter (PM2.5) are important for understanding potential health impacts, prioritizing air pollution mitigation strategies, and enabling global chemical transport model development. PM2.5 filter samples (N ~ 800 from 19 locations) collected from a globally distributed surface particulate matter sampling network (SPARTAN) between January 2013 and April 2019 were analyzed for particulate mass and trace metals content. Metal concentrations exhibited pronounced spatial variation, primarily driven by anthropogenic activities. PM2.5 levels of lead, arsenic, chromium, and zinc were significantly enriched at some locations by factors of 100–3000 compared to crustal concentrations. Levels of metals in PM2.5 and PM10 exceeded health guidelines at multiple sites. For example, Dhaka and Kanpur sites exceeded the US National Ambient Air 3-month Quality Standard for lead (150 ng m−3). Kanpur, Hanoi, Beijing and Dhaka sites had annual mean arsenic concentrations that approached or exceeded the World Health Organization’s risk level for arsenic (6.6 ng m−3). The high concentrations of several potentially harmful metals in densely populated cites worldwide motivates expanded measurements and analyses.

The Negev Desert in Israel is susceptible to frequent atmospheric events of high dust loading which have been linked with negative human health outcomes, including cardiovascular and respiratory distress. Previous research suggests that the highest levels of dust over the region occur during an atmospheric pattern with a cyclone situated over the eastern Mediterranean. This Cyprus Low can bring unsettled weather and strong westerly winds over the Negev. However, while the overall pattern associated with dust events in the Negev Desert is generally well-understood, it remains unclear why days with seemingly similar weather patterns result in different levels of atmospheric dust. Thus, the goal of this study is to better differentiate the atmospheric patterns during dust events over the Negev. Using PM10 data collected in Be’er Sheva, Israel, from 2000 to 2015 in concert with 72-h HYSPLIT back trajectories at three different height levels (surface, 200 m, 500 m), we examine the source region, trajectory groups using a K-Means clustering procedure, and overall synoptic pattern during dust events. Further, we use sea-level pressure data across the region to determine how cyclone strength and location impact dust events in Be’er Sheva. We find that the highest levels of atmospheric dust in the Negev are associated with the Cyprus Low pattern, and air traversing Libya seems to play an especially important role, likely due to the country’s arid surface cover. Cyclone strength is also a critical factor, as lower sea-level pressure results in more severe dust events. A better understanding of the atmospheric features associated with dust events over the Negev Desert will hopefully aid in forecasting these occurrences across the region.

The composition of atmospheric aerosols is dynamic and influenced by their emission sources, organic and inorganic composition, transport pathways, chemical and physical processes, microorganisms' content and more. Characterization of such factors can improve the ability to evaluate air quality and health risks under different atmospheric scenarios. Here we investigate the microbial composition of the atmospheric particulate matter (

Particulate matter (PM), an important component of air pollution, induces significant adverse health effects. Many of the observed health effects caused by inhaled PM are associated with oxidative stress and inflammation. This association has been linked in particular to the particles’ chemical components, especially the inorganic/metal and the organic/polycyclic aromatic hydrocarbon (PAH) fractions, and their ability to generate reactive oxygen species (ROS) in biological systems. The transcription factor NF-E2 nuclear factor erythroid-related factor 2 (Nrf2) is activated by redox imbalance and regulates the expression of phase II detoxifying enzymes. Nrf2 plays a key role in preventing PM-induced toxicity by protecting against oxidative damage and inflammation. This review focuses on specific PM fractions, particularly the dissolved metals and PAH fractions, and their roles in inducing oxidative stress and inflammation in cell and animal models with respect to Nrf2 and mitochondria.

Atmospheric immersion freezing (IF), a heterogeneous ice nucleation process where an ice nucleating particle (INP) is immersed in supercooled water, is a dominant ice formation pathway impacting the hydrological cycle and climate. Implementation of IF derived from field and laboratory data in cloud and climate models is difficult due to the high variability in spatio-temporal scales, INP composition, and morphological complexity. We demonstrate that IF can be consistently described by a stochastic nucleation process accounting for uncertainties in the INP surface area. This approach accounts for time-dependent freezing, a wide range of surface areas and challenges phenomenological descriptions typically used to interpret IF. The results have an immediate impact on the current description, interpretation, and experiments of IF and its implementation in models. The findings are in accord with nucleation theory, and thus should hold for any supercooled liquid material that nucleates in contact with a substrate.

Consumer-level 3D printers emit ultrafine and fine particles, though little is known about their chemical composition or potential toxicity. We report chemical characteristics of the particles in comparison to raw filaments and assessments of particle toxicity. Particles emitted from polylactic acid (PLA) appeared to be largely composed of the bulk filament material with mass spectra similar to the PLA monomer spectra. Acrylonitrile butadiene styrene (ABS), extruded at a higher temperature than PLA, emitted vastly more particles and their composition differed from that of the bulk filament, suggesting that trace additives may control particle formation. In vitro cellular assays and in vivo mice exposure all showed toxic responses when exposed to PLA and ABS-emitted particles, where PLA-emitted particles elicited higher response levels than ABS-emitted particles at comparable mass doses. A chemical assay widely used in ambient air-quality studies showed that particles from various filament materials had comparable particle oxidative potentials, slightly lower than those of ambient particulate matter (PM2.5). However, particle emissions from ABS filaments are likely more detrimental when considering overall exposure due to much higher emissions. Our results suggest that 3D printer particle emissions are not benign and exposures should be minimized.

Nowadays, knowledge regarding component-specific inflammatory effect of fine particulate matter (PM2.5) is limited. In this study, an omics approach based on time-of-flight mass spectrometry was established to identify the key hydrophobic components of PM2.5 associated with pro-inflammatory cytokines released by macrophages after in vitro exposure. Of 764 compounds, 62 components were robustly screened with firmly identified 37 specific chemicals. In addition to polycyclic aromatic hydrocarbons (PAHs) and their methylated congeners, novel oxygen- and nitrogen-containing PAHs and, especially, oxygenated PAHs (Oxy-PAHs) were identified. Interleukin (IL)-6 was associated with Oxy-PAHs of 1,8-naphthalic anhydride, xanthone, and benzo[ h]quinolone, especially, whereas IL-1β and tumor necrosis factor (TNF)-α were associated with most species. Most species were related to IL-1β, which was significantly higher in the heating season, with a monotonic dose-response pattern mainly for Oxy-PAHs and a U-shaped dose-response pattern for primary species. On the basis of the identified components, four sources of pollution (coal combustion, traffic emissions, biomass burning, and secondary formation, traced by Oxy-PAHs such as 1,8-naphthalic anhydride and quinones) were resolved by the positive matrix factorization model. TNF-α was associated with primary sources, whereas IL-1β and IL-6 were associated with both primary and secondary sources, suggesting different inflammatory effects between primary and secondary sources when assessing the toxicity-driven disparities of known and unknown PM2.5 components.

Polycyclic aromatic hydrocarbons (PAHs) are toxic organic trace components in atmospheric aerosols that have impacts on climate and human health. They are bound to airborne particles and transported over long distances. Observations of their distribution, transport pathways, and degradation are crucial for risk assessment and mitigation. Such estimates would benefit from online detection of PAHs along with analysis of the carrying particles to identify the source. Typically, laser desorption/ionization (LDI) in a bipolar mass spectrometer reveals the inorganic constituents and provides limited molecular information. In contrast, two-step ionization approaches produce detailed PAH mass spectra from individual particles but without the source-specific inorganic composition. Here we report a new technique that yields the single-particle PAH composition along with both positive and negative inorganic ions via LDI. Thus, the complete particle characterization and source apportionment from conventional bipolar LDI-analysis becomes possible, combined with a detailed PAH spectrum for the same particle. The key idea of the method is spatiotemporal matching of the ionization laser pulse to the transient component distribution in the particle plume after laser desorption. The technique is robust and field-deployable with only slightly higher costs and complexity compared to two-step approaches. We demonstrate its capability to reveal the PAH-distribution on different particle types in combustion aerosols and ambient air.

Criegee intermediates (CI) from ozonolysis of biogenic volatile organic compounds (BVOC) have been suggested to be important atmospheric oxidants. However, due to their low atmospheric concentrations, possible high reactivity with water vapor, and unconstrained thermal unimolecular decay rates, their impact on atmospheric oxidation of trace species such as SO2 and NO2 remains uncertain. In this study, we investigate the formation of secondary sulfate aerosols (SSA) in nocturnal power plant plumes in the Southeastern US. These plumes have large mixing ratios of SO2 and NO that make reaction with CI competitive with other pathways, such as thermal unimolecular decay and water vapor reaction. The background into which these plumes are emitted has high levels of BVOC and O-3, whose reaction produces a large source of CI. Observed nighttime power plant plume intercepts had measurable sulfate aerosol, ranging from 0.7-1.2% of the total plume sulfur (SO2 + sulfate) on a molar basis. In the absence of photochemical OH oxidation, these observed sulfate levels can be compared to calculated CI + SO2 production. We present a plume dispersion model that simulates the chemical evolution of these nighttime plumes and compare the results to observed sulfate aerosol. Thermal unimolecular decay of CI is the largest uncertainty. In the absence of thermal unimolecular CI decay, CI reactions with SO2 in the dark account for up to 41% of the total observed sulfate aerosol, with the remainder attributable to reaction of SO2 with secondary OH and direct emission. Conversely, with a thermal unimolecular decay rate for all CI of 200 s(-1), equivalent to the highest measured rate, CI reactions with SO2 accounted for only S.7% of the total SSA. A second uncertainty is the rate coefficients for larger, and as yet unmeasured, CI species. The most important CI in the modeled scenario is the C, compound, CH2OO, which accounts for up to 50% of the CIs produced from isoprene. C-4 CIs may contribute up to 40% of the CIs produced and are expected to have substantially slower thermal unimolecular decay rates and water vapor reaction rate coefficients. Therefore, the model results may be a lower limit to the CI contribution to SSA. Calculated nighttime (10 h) total SO2 oxidation was 1.8%, of which 1.1% was due to CI + SO2, and the remainder to secondary OH + SO2. This compares to daytime (14 h) SO2 oxidation rates of 4% due to photochemical OH + SO2 reaction.

Several types of natural molecules interact specifically with ice crystals. Small antifreeze proteins (AFPs) adsorb to particular facets of ice crystals, thus inhibiting their growth, whereas larger ice-nucleating proteins (INPs) can trigger the formation of new ice crystals at temperatures much higher than the homogeneous ice nucleation temperature of pure water. It has been proposed that both types of proteins interact similarly with ice and that, in principle, they may be able to exhibit both functions. Here we investigated two naturally occurring antifreeze proteins, one from fish, type-III AFP, and one from beetles, TmAFP. We show that in addition to ice growth inhibition, both can also trigger ice nucleation above the homogeneous freezing temperature, providing unambiguous experimental proof for their contrasting behavior. Our analysis suggests that the predominant difference between AFPs and INPs is their molecular size, which is a very good predictor of their ice nucleation temperature.

The second phase of the Fifth International Ice Nucleation Workshop (FIN-02) involved the gathering of a large number of researchers at the Karlsruhe Institute of Technology's Aerosol Interactions and Dynamics of the Atmosphere (AIDA) facility to promote characterization and understanding of ice nucleation measurements made by a variety of methods used worldwide. Compared to the previous workshop in 2007, participation was doubled, reflecting a vibrant research area. Experimental methods involved sampling of aerosol particles by direct processing ice nucleation measuring systems from the same volume of air in separate experiments using different ice nucleating particle (INP) types, and collections of aerosol particle samples onto filters or into liquid for sharing amongst measurement techniques that post-process these samples. In this manner, any errors introduced by differences in generation methods when samples are shared across laboratories were mitigated. Furthermore, as much as possible, aerosol particle size distribution was controlled so that the size limitations of different methods were minimized. The results presented here use data from the workshop to assess the comparability of immersion freezing measurement methods activating INPs in bulk suspensions, methods that activate INPs in condensation and/or immersion freezing modes as single particles on a substrate, continuous flow diffusion chambers (CFDCs) directly sampling and processing particles well above water saturation to maximize immersion and subsequent freezing of aerosol particles, and expansion cloud chamber simulations in which liquid cloud droplets were first activated on aerosol particles prior to freezing. The AIDA expansion chamber measurements are expected to be the closest representation to INP activation in atmospheric cloud parcels in these comparisons, due to exposing particles freely to adiabatic cooling.The different particle types used as INPs included the minerals illite NX and potassium feldspar (K-feldspar), two natural soil dusts representative of arable sandy loam (Argentina) and highly erodible sandy dryland (Tunisia) soils, respectively, and a bacterial INP (Snomax (R)). Considered together, the agreement among post-processed immersion freezing measurements of the numbers and fractions of particles active at different temperatures following bulk collection of particles into liquid was excellent, with possible temperature uncertainties inferred to be a key factor in determining INP uncertainties. Collection onto filters for rinsing versus directly into liquid in impingers made little difference. For methods that activated collected single particles on a substrate at a controlled humidity at or above water saturation, agreement with immersion freezing methods was good in most cases, but was biased low in a few others for reasons that have not been resolved, but could relate to water vapor competition effects. Amongst CFDC-style instruments, various factors requiring (variable) higher supersaturations to achieve equivalent immersion freezing activation dominate the uncertainty between these measurements, and for comparison with bulk immersion freezing methods. When operated above water saturation to include assessment of immersion freezing, CFDC measurements often measured at or above the upper bound of immersion freezing device measurements, but often underestimated INP concentration in comparison to an immersion freezing method that first activates all particles into liquid droplets prior to cooling (the PIMCA-PINC device, or Portable Immersion Mode Cooling chAmber-Portable Ice Nucleation Chamber), and typically slightly underestimated INP number concentrations in comparison to cloud parcel expansions in the AIDA chamber; this can be largely mitigated when it is possible to raise the relative humidity to sufficiently high values in the CFDCs, although this is not always possible operationally.Correspondence of measurements of INPs among direct sampling and post-processing systems varied depending on the INP type. Agreement was best for Snomax (R) particles in the temperature regime colder than 10 degrees C, where their ice nucleation activity is nearly maximized and changes very little with temperature. At temperatures warmer than -10 degrees C, Snomax (R) INP measurements (all via freezing of suspensions) demonstrated discrepancies consistent with previous reports of the instability of its protein aggregates that appear to make it less suitable as a calibration INP at these temperatures. For Argentinian soil dust particles, there was excellent agreement across all measurement methods; measures ranged within 1 order of magnitude for INP number concentrations, active fractions and calculated active site densities over a 25 to 30 degrees C range and 5 to 8 orders of corresponding magnitude change in number concentrations. This was also the case for all temperatures warmer than -25 degrees C in Tunisian dust experiments. In contrast, discrepancies in measurements of INP concentrations or active site densities that exceeded 2 orders of magnitude across a broad range of temperature measurements found at temperatures warmer than- 25 degrees C in a previous study were replicated for illite NX. Discrepancies also exceeded 2 orders of magnitude at temperatures of -20 to -25 degrees C for potassium feldspar (K-feldspar), but these coincided with the range of temperatures at which INP concentrations increase rapidly at approximately an order of magnitude per 2 degrees C cooling for K-feldspar.These few discrepancies did not outweigh the overall positive outcomes of the workshop activity, nor the future utility of this data set or future similar efforts for resolving remaining measurement issues. Measurements of the same materials were repeatable over the time of the workshop and demonstrated strong consistency with prior studies, as reflected by agreement of data broadly with parameterizations of different specific or general (e.g., soil dust) aerosol types. The divergent measurements of the INP activity of illite NX by direct versus post-processing methods were not repeated for other particle types, and the Snomax (R) data demonstrated that, at least for a biological INP type, there is no expected measurement bias between bulk collection and direct immediately processed freezing methods to as warm as -10 degrees C. Since particle size ranges were limited for this workshop, it can be expected that for atmospheric populations of INPs, measurement discrepancies will appear due to the different capabilities of methods for sampling the full aerosol size distribution, or due to limitations on achieving sufficient water supersaturations to fully capture immersion freezing in direct processing instruments. Overall, this workshop presents an improved picture of present capabilities for measuring INPs than in past workshops, and provides direction toward addressing remaining measurement issues.

Exposure to ambient fine particulate matter (PM
2.5) is a leading risk factor for the global burden of disease. However, uncertainty remains about PM
2.5 sources. We use a global chemical transport model (GEOS-Chem) simulation for 2014, constrained by satellite-based estimates of PM
2.5 to interpret globally dispersed PM
2.5 mass and composition measurements from the ground-based surface particulate matter network (SPARTAN). Measured site mean PM
2.5 composition varies substantially for secondary inorganic aerosols (2.4-19.7 μg/m
3), mineral dust (1.9-14.7 μg/m
3), residual/organic matter (2.1-40.2 μg/m
3), and black carbon (1.0-7.3 μg/m
3). Interpretation of these measurements with the GEOS-Chem model yields insight into sources affecting each site. Globally, combustion sectors such as residential energy use (7.9 μg/m
3), industry (6.5 μg/m
3), and power generation (5.6 μg/m
3) are leading sources of outdoor global population-weighted PM
2.5 concentrations. Global population-weighted organic mass is driven by the residential energy sector (64%) whereas population-weighted secondary inorganic concentrations arise primarily from industry (33%) and power generation (32%). Simulation-measurement biases for ammonium nitrate and dust identify uncertainty in agricultural and crustal sources. Interpretation of initial PM
2.5 mass and composition measurements from SPARTAN with the GEOS-Chem model constrained by satellite-based PM
2.5 provides insight into sources and processes that influence the global spatial variation in PM
2.5 composition.

Sea spray aerosols (SSA), have a profound effect on the climate; however, the contribution of oceanic microbial activity to SSA is not fully established. We assessed aerosolization of the calcite units (coccoliths) that compose the exoskeleton of the cosmopolitan bloom-forming coccolithophore, Emiliania huxleyi. Airborne coccolith emission occurs in steady-state conditions and increases by an order of magnitude during E. huxleyi infection by E. huxleyi virus (EhV). Airborne to seawater coccolith ratio is 1:108, providing estimation of airborne concentrations from seawater concentrations. The coccoliths' unique aerodynamic structure yields a characteristic settling velocity of ∼0.01 cm s-1, ∼25 times slower than average sea salt particles, resulting in coccolith fraction enrichment in the air. The calculated enrichment was established experimentally, indicating that coccoliths may be key contributors to coarse mode SSA surface area, comparable with sea salt aerosols. This study suggests a coupling between key oceanic microbial interactions and fundamental atmospheric processes like SSA formation.

Atmospheric photooxidation of isoprene forms isoprene epoxydiols (IEPOX) and hydroxymethel-methyl-α-lactone (HMML) via hydroperoxyl radical (HO
2) channel and NO/NO
2 channel, respectively. Reactive uptake of these epoxides onto particles produces isoprene secondary organic aerosols (iSOA). Currently, there is little information regarding these two epoxides during iSOA formation in polluted regions. In this study, iSOA tracers from IEPOX and HMML were measured from summer to fall in the heavily polluted Pearl River Delta (PRD) region. The total concentration of the iSOA tracers ranged from 5.77 to 466 ng m
−3. Isoprene SOA tracers correlated well with sulfate (p 22 °C) suppresses the production of HMML, likely as a result of fast decomposition of HMML's precursor under high temperatures. Thus, the HMML-derived tracers had lower levels than the IEPOX-derived SOA tracers during the whole campaign. The ratios of the IEPOX-derived tracers to the HMML-derived SOA tracers in summer were ~3 times higher than those in fall. This seasonal trend may be explained by the relative high isoprene/NO
x ratio, temperature, and fast heterogeneous reaction of IEPOX in summer. Our study shows that in highly polluted regions like PRD, reduction in SO
2 emission can significantly reduce iSOA formation.

Exposure to air pollution can induce oxidative stress, inflammation and adverse health effects. To understand how seasonal and chemical variations drive health impacts, we investigated indications for oxidative stress and inflammation in mice exposed to water and organic extracts from urban fine particles/PM2.5 (particles with aerodynamic diameter ≤ 2.5 μm) collected in Beijing, China. Higher levels of pollution components were detected in heating season (HS, winter and part of spring) PM2.5 than in the non-heating season (NHS, summer and part of spring and autumn) PM2.5. HS samples were high in metals for the water extraction and high in polycyclic aromatic hydrocarbons (PAHs) for the organic extraction compared to their controls. An increased inflammatory response was detected in the lung and liver following exposure to the organic extracts compared to the water extracts, and mostly in the HS PM2.5. While reduced antioxidant response was observed in the lung, it was activated in the liver, again, more in the HS extracts. Nrf2 transcription factor, a master regulator of stress response that controls the basal oxidative capacity and induces the expression of antioxidant response, and its related genes were induced. In the liver, elevated levels of lipid peroxidation adducts were measured, correlated with histologic analysis that revealed morphologic features of cell damage and proliferation, indicating oxidative and toxic damage. In addition, expression of genes related to detoxification of PAHs was observed. Altogether, the study suggests that the acute effects of PM2.5 can vary seasonally with stronger health effects in the HS than in the NHS in Beijing, China and that some secondary organs may be susceptible for the exposure damage. Specifically, the liver is a potential organ influenced by exposure to organic components such as PAHs from coal or biomass burning and heating.

The wavelength-dependence of the complex refractive indices (RI) in the visible spectral range of secondary organic aerosols (SOA) are rarely studied, and the evolution of the RI with atmospheric aging is largely unknown. In this study, we applied a novel white light-broadband cavity enhanced spectroscopy to measure the changes in the RI (400650 nm) of beta-pinene and p-xylene SOA produced and aged in an oxidation flow reactor, simulating daytime aging under NOx-free conditions. It was found that these SOA are not absorbing in the visible range, and that the real part of the RI, n, shows a slight spectral dependence in the visible range. With increased OH exposure, n first increased and then decreased, possibly due to an increase in aerosol density and chemical mean polarizability for SOA produced at low OH exposures, and a decrease in chemical mean polarizability for SOA produced at high OH exposures, respectively. A simple radiative forcing calculation suggests that atmospheric aging can introduce more than 40% uncertainty due to the changes in the RI for aged SOA.

Lag Ba'Omer, a nationwide bonfire festival in Israel, was chosen as a case study to investigate the influence of a major biomass burning event on the light absorption properties of atmospheric brown carbon (BrC). The chemical composition and optical properties of BrC chromophores were investigated using a high performance liquid chromatography (HPLC) platform coupled to photo diode array (PDA) and high resolution mass spectrometry (HRMS) detectors. Substantial increase of BrC light absorption coefficient was observed during the night-long, biomass burning event. Most chromophores observed during the event were attributed to nitroaromatic compounds (NAC), comprising 28 elemental formulas of at least 63 structural isomers. The NAC, in combination, accounted for 50-80% of the total visible light absorption (> 400 nm) by solvent extractable BrC. The results highlight that NAC, in particular nitrophenols, are important light absorption contributors of biomass burning organic aerosol (BBOA), suggesting that night time chemistry of center dot NO3 and N2O5 with particles may play a significant role in atmospheric transformations of BrC. Nitrophenols and related compounds were especially important chromophores of BBOA. The absorption spectra of the BrC chromophores are influenced by the extraction solvent and solution pH, implying that the aerosol acidity is an important factor controlling the light absorption properties of BrC.

Y. Rudich remarked: About comparisons between biogenic and anthropogenic SOA, in terms of potency to have a biological effect, chamber studies suggest that anthropogenic SOA is more toxic and leads to more mortality than BSOA.1,2 Can you bridge the gap between your conclusions and these studies?1 W. Y. Tuet et al., Atmos. Chem. Phys., 2017, 17, 839–853.2 V. Verma et al., Environ. Sci. Technol., 2017, 51, 3128–3137

Yinon Rudich commented: I would be cautious in inferring that exposure to ozone and NO2, that leads to nitration and oligomerization, necessarily increases allergenicity. Over a long time period proteins may lose their ability to induce allergies. I would advise direct allergenicity tests to verify this conclusion.1 1 N. Lang-Yona, T. Shuster-Meiseles, Y. Mazar, O. Yarden and Y. Rudich, Impact of urban air pollution on the allergenicity of Aspergillus fumigatus conidia: Outdoor exposure study supported by laboratory, Sci. Total Environ., 2016, 541, 365–371.

Microorganisms carried by dust storms are transported through the atmosphere and may affect human health and the functionality of microbial communities in various environments. Characterizing the dust-borne microbiome in dust storms of different origins or that followed different trajectories provides valuable data to improve our understanding of global health and environmental impacts. We present a comparative study on the diversity of dust-borne bacterial communities in dust storms from three distinct origins (North Africa, Syria and Saudi Arabia) and compare them with local bacterial communities sampled on clear days, all collected at a single location: Rehovot, Israel. Storms from different dust origins exhibited distinct bacterial communities, with signature bacterial taxa. Dust storms were characterized by a lower abundance of selected antibiotic resistance genes (ARGs) compared with ambient dust, asserting that the origin of these genes is local and possibly anthropogenic. With the progression of the storm, the storm-borne bacterial community showed increasing resemblance to ambient dust, suggesting mixing with local dust. These results show, for the first time, that dust storms from different sources display distinct bacterial communities, suggesting possible diverse effects on the environment and public health.

The multi-pass photoacoustic spectrometer (PAS) is an important tool for the direct measurement of light absorption by atmospheric aerosol. Accurate PAS measurements heavily rely on accurate calibration of their signal. Ozone is often used for calibrating PAS instruments by relating the photoacoustic signal to the absorption coefficient measured by an independent method such as cavity ring down spectroscopy (CRD-S), cavity-enhanced spectroscopy (CES) or an ozone monitor. We report here a calibration method that uses measured absorption coefficients of aerosolized, light-absorbing organic materials and offer an alternative approach to calibrate photoacoustic aerosol spectrometers at 404 nm. To implement this method, we first determined the complex refractive index of nigrosin, an organic dye, using spectroscopic ellipsometry and then used this well-characterized material as a standard material for PAS calibration.

Exposure to ambient particulate matter (PM), including PM from resuspension of soils and dusts, increases the risk for respiratory diseases. However, the exact mechanism of PM-mediated damage to the lungs remains unclear. Due to recent increases in the frequency of dust storms in many areas, we examined the cytotoxic effects of soil-dust samples collected in an arid zone in Israel on rat lung macrophages. The desert soil contains soil crusts and low levels of toxic metal content. Exposure of cells to water extracts from the dust samples caused significant reduction in the concentration of live cells and overall cell viability. The dust samples induced cell death through apoptosis, mitochondrial dysfunction, and increased mitochondrial lipid peroxidation. The dust samples generated more reactive oxygen species (ROS) compared to control-treated samples and National Institute of Standards and Technology San Joaquin Valley standard reference material. To assess whether the oxidative imbalance induced by dust extract also interferes with the antioxidant defense, we evaluated phase II detoxifying and antioxidant enzymes, which are Nrf2 classical targets. The Nrf2 transcription factor is a master regulator of cellular adaptation to stress. The dust extracts produced a significant increase in phase II detoxifying genes. This work suggests that the health-related injury observed in rat lung cells exposed to dust extracts is associated with ROS generation, mitochondrial dysfunction, mitochondrial lipid peroxidation, and cellular antioxidant imbalance. Damage to lung mitochondria may be an important mechanism by which dust-containing bacterial material induces lung injury upon inhalation.

Anthropogenic activities are responsible for the emission of gaseous and particulate pollutants that modify atmospheric composition. Such changes are, in turn, responsible for the degradation of air quality at the regional/local scale as well as for changes of climate. Air pollution and climate change are two intimately connected environmental issues. However, these two environmental challenges are still viewed as separate issues, which are dealt with by different science communities and within different policy frameworks. Indeed, many mitigation options offer the possibility to both improve air quality and mitigate climate change but, at the same time, mitigation options that may provide benefits to one aspect, are worsening the situation in the other. Therefore, coordinated actions taking into account the air quality-climate linkages are required. These actions need to be based on strong scientific grounds, as recognised by the European Commission that in the past few years has promoted consultation processes among the science community, the policy makers and the relevant stakeholders. Here, the main fields in which such coordinated actions are needed are examined from a policy perspective. (C) 2016 Elsevier Ltd. All rights reserved.

Atmospheric aerosols play an important part in the Earth's energy budget by scattering and absorbing incoming solar and outgoing terrestrial radiation. To quantify the effective radiative forcing due to aerosol-radiation interactions, researchers must obtain a detailed understanding of the spectrally dependent intensive and extensive optical properties of different aerosol types. Our new approach retrieves the optical coefficients and the single-scattering albedo of the total aerosol population over 300 to 650 nm wavelength, using extinction measurements from a broadband cavity-enhanced spectrometer at 315 to 345 nm and 390 to 420 nm, extinction and absorption measurements at 404 nm from a photoacoustic cell coupled to a cavity ring-down spectrometer, and scattering measurements from a three-wavelength integrating nephelometer. By combining these measurements with aerosol size distribution data, we retrieved the time-and wavelength-dependent effective complex refractive index of the aerosols. Retrieval simulations and laboratory measurements of brown carbon proxies showed low absolute errors and good agreement with expected and reported values. Finally, we implemented this new broadband method to achieve continuous spectral-and time-dependent monitoring of ambient aerosol population, including, for the first time, extinction measurements using cavity-enhanced spectrometry in the 315 to 345 nm UV range, in which significant light absorption may occur.

We evaluated the impact of Saharan dust storms on the local airborne microbiome in a city in the Eastern Mediterranean area. Samples of particles with diameter less than 10 mum were collected during two spring seasons on both dusty and nondusty days. DNA was extracted, and partial 16S rRNA gene amplicons were sequenced using the Illumina platform. Bioinformatic analysis showed the effect of dust events on the diversity of the atmospheric microbiome. The relative abundance of desert soil-associated bacteria increased during dust events, while the relative abundance of anthropogenic-influenced taxa decreased. Quantitative polymerase chain reaction measurements of selected clinically significant antibiotic resistance genes (ARGs) showed that their relative abundance decreased during dust events. The ARG profiles on dust-free days were similar to those in aerosol collected in a poultry house, suggesting a strong agricultural influence on the local ambient profiles. We conclude that dust storms enrich the ambient airborne microbiome with new soil-derived bacteria that disappear as the dust settles, suggesting that the bacteria are transported attached to the dust particles. Dust storms do not seem to be an important vector for transport of probed ARGs.

Exposure to particulate matter (PM) pollution in cities and urban canyons can be harmful to the exposed population. However, the underlying mechanisms that lead to health effects are not yet elucidated. It is postulated that exposure to repeated, small, environmentally relevant concentrations can affect lung homeostasis. This study examines the impact of repeated exposures to urban PM on mouse lungs with focus on inflammatory and oxidative stress parameters. Aqueous extracts from collected urban PM were administered to mice by 5 repeated intra-tracheal instillations (IT). Multiple exposures, led to an increase in cytokine levels in both bronchoalveolar lavage fluid and in the blood serum, indicating a systemic reaction. Lung mRNA levels of antioxidant/phase II detoxifying enzymes decreased by exposure to the PM extract, but not when metals were removed by chelation. Finally, disruption of lung tissue oxidant-inflammatory/defense balance was evidenced by increased levels of lipid and protein oxidation. Unlike response to a single IT exposure to the same dose and source of extract, multiple exposures result in lung oxidative damage and a systemic inflammatory reaction. These could be attributed to compromised capacity to activate the protective Nrf2 tissue defense system. It is suggested that water-soluble metals present in urban PM, potentially from break and tire wear, may constitute major drivers of the pulmonary and systemic responses to multiple exposure to urban PM.

Outdoor aerosol research commonly uses particulate matter sampled on filters. This procedure enables various characterizations of the collected particles to be performed in parallel. The purpose of the method presented here is to obtain a highly accurate and reliable analysis of the endotoxin and DNA content of bio-aerosols extracted from filters. The extraction of high molecular weight organic molecules, such as lipopolysaccharides, from sampled filters involves shaking the sample in a pyrogen-free water-based medium. The subsequent analysis is based on an enzymatic reaction that can be detected using a turbidimetric measurement. As a result of the high organic content on the sampled filters, the extraction of DNA from the samples is performed using a commercial DNA extraction kit that was originally designed for soils and modified to improve the DNA yield. The detection and quantification of specific microbial species using quantitative polymerase chain reaction (q-PCR) analysis are described and compared with other available methods.

Interaction of biogenic volatile organic compounds (VOCs) with Anthropogenic VOC (AVOC) affects the physicochemical properties of secondary organic aerosol (SOA). We investigated cloud droplet activation (CCN activity), droplet growth kinetics, and hygroscopicity of mixed anthropogenic and biogenic SOA (ABSOA) compared to pure biogenic SOA (BSOA) and pure anthropogenic SOA (ASOA). Selected monoterpenes and aromatics were used as representative precursors of BSOA and ASOA, respectively.We found that BSOA, ASOA, and ABSOA had similar CCN activity despite the higher oxygen to carbon ratio (O/C) of ASOA compared to BSOA and ABSOA. For individual reaction systems, CCN activity increased with the degree of oxidation. Yet, when considering all different types of SOA together, the hygroscopicity parameter, kappa(CCN), did not correlate with O/C. Droplet growth kinetics of BSOA, ASOA, and ABSOA were comparable to that of (NH4)(2)SO4, which indicates that there was no delay in the water uptake for these SOA in supersaturated conditions.In contrast to CCN activity, the hygroscopicity parameter from a hygroscopic tandem differential mobility analyzer (HTDMA) measurement, kappa(HTDMA) of ASOA was distinctively higher (0.09-0.10) than that of BSOA (0.030-0.06), which was attributed to the higher degree of oxida-tion of ASOA. The ASOA components in mixed ABSOA enhanced aerosol hygroscopicity. Changing the ASOA fraction by adding biogenic VOC (BVOC) to ASOA or vice versa (AVOC to BSOA) changed the hygroscopicity of aerosol, in line with the change in the degree of oxidation of aerosol. However, the hygroscopicity of ABSOA cannot be described by a simple linear combination of pure BSOA and ASOA systems. This indicates that additional processes, possibly oligomerization, affected the hygroscopicity.Closure analysis of CCN and HTDMA data showed kappa(HTDMA) was lower than kappa(CCN) by 30-70 %. Better closure was achieved for ASOA compared to BSOA. This discrepancy can be attributed to several reasons. ASOA seemed to have higher solubility in subsaturated conditions and/or higher surface tension at the activation point than that of BSOA.

New measurements of water diffusion in secondary organic aerosol (SOA) material produced by oxidation of alpha-pinene and in a number of organic/inorganic model mixtures (3-methylbutane-1,2,3-tricarboxylic acid (3-MBTCA), levoglucosan, levoglucosan/NH4HSO4, raffinose) are presented. These indicate that water diffusion coefficients are determined by several properties of the aerosol substance and cannot be inferred from the glass transition temperature or bouncing properties. Our results suggest that water diffusion in SOA particles is faster than often assumed and imposes no significant kinetic limitation on water uptake and release at temperatures above 220 K. The fast diffusion of water suggests that heterogeneous ice nucleation on a glassy core is very unlikely in these systems. At temperatures below 220 K, model simulations of SOA particles suggest that heterogeneous ice nucleation may occur in the immersion mode on glassy cores which remain embedded in a liquid shell when experiencing fast updraft velocities. The particles absorb significant quantities of water during these updrafts which plasticize their outer layers such that these layers equilibrate readily with the gas phase humidity before the homogeneous ice nucleation threshold is reached. Glass formation is thus unlikely to restrict homogeneous ice nucleation. Only under most extreme conditions near the very high tropical tropopause may the homogeneous ice nucleation rate coefficient be reduced as a consequence of slow condensed-phase water diffusion. Since the differences between the behavior limited or non limited by diffusion are small even at the very high tropical tropopause, condensed-phase water diffusivity is unlikely to have significant consequences on the direct climatic effects of SOA particles under tropospheric conditions.

Inhalation of traffic-associated atmospheric particulate matter (PM2.5) is recognized as a significant health risk. In this study, we focused on a single ("subclinical response") exposure to water-soluble extracts from PM collected at a roadside site in a major European city to elucidate potential components that drive pulmonary inflammatory, oxidative, and defense mechanisms and their systemic impacts. Intratracheal instillation (IT) of the aqueous extracts induced a 24 h inflammatory response characterized by increased broncho-alveolar lavage fluid (BALF) cells and cytokines (IL-6 and TNF-alpha), increased reactive oxygen species production, but insignificant lipids and proteins oxidation adducts in mouse lungs. This local response was largely self-resolved by 48 h, suggesting that it could represent a subclinical response to everyday-level exposure. Removal of soluble metals by chelation markedly diminished the pulmonary PM-mediated response. An artificial metal solution (MS) recapitulated the PM extract response. The self-resolving nature of the response is associated with activating defense mechanisms (increased levels of catalase and glutathione peroxidase expression), observed with both PM extract and MS. In conclusion, metals present in PM collected near roadways are largely responsible for the observed transient local pulmonary inflammation and oxidative stress. Simultaneous activation of the antioxidant defense response may protect against oxidative damage.

The Amazon basin is a hot spot of anthropogenically-driven biomass burning, accounting for approximately 15% of total global fire emissions. It is essential to accurately measure these fires for robust regional and global modeling of key environmental processes. Here we have explored the link between spatio-temporal variability patterns in the Amazon basin's fires and the resulting smoke loading using 11 years (2002-2012) of data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Aerosol Robotic Network (AERONET) observations. Focusing on the peak burning season (July-October), our analysis shows strong inter-annual correlation between aerosol optical depth (AOD) and two MODIS fire products: fire radiative power (FRP) and fire pixel counts (FC). Among these two fire products, the FC better indicates the amount of smoke in the basin, as represented in remotely sensed AOD data. This fire product is significantly correlated both with regional AOD retrievals from MODIS and with point AOD measurements from the AERONET stations, pointing to spatial homogenization of the smoke over the basin on a seasonal time scale. However, MODIS AODs are found better than AERONET AODs observation for linking between smoke and fire. Furthermore, MODIS AOD measurements are strongly correlated with number of fires similar to 1(0)-2(0) to the east, most likely due to westward advection of smoke by the wind. These results can be rationalized by the regional topography and the wind regimes. Our analysis can improve data assimilation of satellite and ground-based observations into regional and global model studies, thus improving the assessment of the environmental and climatic impacts of frequency and distribution variability of the Amazon basin's fires. We also provide the optimal spatial and temporal scales for ground-based observations, which could be used for such applications. (C) 2015 Elsevier Ltd. All rights reserved.

Background: Over the last decade, there is growing evidence that exposure to air pollution may be associated with increased risk for congenital malformations. Objectives: To evaluate the possible association between exposures to air pollution during pregnancy and congenital malformations among infants born following spontaneously conceived (SC) pregnancies and assisted reproductive technology (ART) pregnancies. Methods: This is an historical cohort study comprising 216,730 infants: 207,825 SC infants and 8905 ART conceived infants, during the periods 1997-2004. Air pollution data including sulfur dioxide (SO2), particulate matter

To evaluate the health impacts of particulate matter and develop effective pollutant abatement strategies, one needs to know the source contributions to the observed concentrations. The most common approach involves the collection of ambient air samples on filters, laboratory analyses to quantify the chemical composition, and application of receptor modeling methods. This approach is expensive and time consuming and limits the ability to monitor the temporal and spatial impacts from different pollutant sources. An alternative method for apportioning the sources of ambient PM is the application of microscopic chemical imaging (MCI). The MCI method involves measuring individual particle's fluorescence and source attribution is based on the individual particle analysis coupled with identification from a source library. Using this approach, the apportionment of ambient PM can be performed in near real time, which allows for the generation of temporal and spatial maps of pollutant source impacts in an urban area. (C) 2013 Elsevier B.V. All rights reserved.

Using shipboard and satellite measurements we explore the environmental factors affecting the number concentration of aerosols with diameter 100

We examined fungal communities associated with the PM10 mass of Rehovot, Israel outdoor air samples collected in the spring and fall seasons. Fungal communities were described by 454 pyrosequencing of the internal transcribed spacer (ITS) region of the fungal ribosomal RNA encoding gene. To allow for a more quantitative comparison of fungal exposure in humans, the relative abundance values of specific taxa were transformed to absolute concentrations through multiplying these values by the sample's total fungal spore concentration (derived from universal fungal qPCR). Next, the sequencing-based absolute concentrations for Alternaria alternata, Cladosporium cladosporioides, Epicoccum nigrum, and Penicillium/ Aspergillus spp. were compared to taxon-specific qPCR concentrations for A. alternata, C. cladosporioides, E. nigrum, and Penicillium/Aspergillus spp. derived from the same spring and fall aerosol samples. Results of these comparisons showed that the absolute concentration values generated from pyrosequencing were strongly associated with the concentration values derived from taxon-specific qPCR (for all four species, p 0.70). The correlation coefficients were greater for species present in higher concentrations. Our microbial aerosol population analyses demonstrated that fungal diversity (number of fungal operational taxonomic units) was higher in the spring compared to the fall (p = 0.02), and principal coordinate analysis showed distinct seasonal differences in taxa distribution (ANOSIM p = 0.004). Among genera containing allergenic and/or pathogenic species, the absolute concentrations of Alternaria, Aspergillus, Fusarium, and Cladosporium were greater in the fall, while Cryptococcus, Penicillium, and Ulocladium concentrations were greater in the spring. The transformation of pyrosequencing fungal population relative abundance data to absolute concentrations can improve next-generation DNA sequencing-based quantitative aerosol exposure asse

The effects of absorbing aerosols on the atmospheric radiation budget and dynamics over the eastern Mediterranean region are studied using satellites and ground-based observations, and radiative transfer model calculations, under summer conditions. Climatology of aerosol optical depth (AOD), single scattering albedo (SSA) and size parameters were analyzed using multiyear (1999-2012) observations from Moderate Resolution Imaging Spectroradiometer (MODIS), Multi-angle Imaging SpectroRadiometer (MISR) and AErosol RObotic NET-work (AERONET). Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP)-derived aerosol vertical distributions and their classifications are used to calculate the AOD of four dominant aerosol types: dust, polluted dust, polluted continental, and marine aerosol over the region. The seasonal mean (June-August 2010) AODs are 0.22 +/- 0.02, 0.11 +/- 0.04, 0.10 +/- 0.04 and 0.06 +/- 0.01 for polluted dust, polluted continental, dust and marine aerosol, respectively. Changes in the atmospheric temperature profile as a function of absorbing aerosol loading were derived for the same period using observations from the AIRS satellite. We inferred heating rates in the aerosol layer of similar to 1.7 +/- 0.8 K day(-1) between 925 and 850 hPa, which is attributed to aerosol absorption of incoming solar radiation. Radiative transfer model (RTM) calculations show significant atmospheric warming for dominant absorbing aerosol over the region. A maximum atmospheric forcing of +16.7 +/- 7.9 W m(-2) is calculated in the case of polluted dust, followed by dust (+9.4 +/- 4.9 W m(-2)) and polluted continental (+6.4 +/- 4.5 W m(-2)). RTM-derived heating rate profiles for dominant absorbing aerosol show warming of 0.1-0.9 K day(-1) in the aerosol layer (

The impact of nitrogen oxides (NOx = NO+NO2) on new particle formation (NPF) and on photochemical ozone production from real plant volatile organic compound (BVOC) emissions was studied in a laboratory setup. At high NOx conditions ([BVOC]/[NOx] 23 ppb) new particle formation was suppressed. Instead, photochemical ozone formation was observed resulting in higher hydroxyl radical (OH) and lower nitrogen monoxide (NO) concentrations. When [NO] was reduced back to levels below 1 ppb by OH reactions, NPF was observed. Adding high amounts of NOx caused NPF to be slowed by orders of magnitude compared to analogous experiments at low NOx conditions ([NOx] similar to 300 ppt), although OH concentrations were higher. Varying NO2 photolysis enabled showing that NO was responsible for suppression of NPF. This suggests that peroxy radicals are involved in NPF. The rates of NPF and photochemical ozone production were related by power law dependence with an exponent approaching -2. This exponent indicated that the overall peroxy radical concentration must have been similar when NPF occurred. Thus, permutation reactions of first-generation peroxy radicals cannot be the rate limiting step in NPF from monoterpene oxidation. It was concluded that permutation reactions of higher generation peroxyradical-like intermediates limit the rate of new particle formation. In contrast to the strong effects on the particle numbers, the formation of particle mass was substantially less sensitive to NOx concentrations. If at all, yields were reduced by about an order of magnitude only at very high NOx concentrations.

This special issue of the Journal of Physical Chemistry C honors Professor Ron Naaman, the Aryeh and Mintzi Katzman Professor at the Weizmann Institute of Science. Ron has made pioneering contributions to our understanding of molecular physics and the quantum nature of matter through the creative design of experiments that address fundamental physical questions about molecules and molecular assemblies. We are grateful to the editors and staff of the Journal and to all of the contributors to this special issue for making it possible to recognize Ron in this way.

Increased susceptibility to allergies has been documented in the Western world in recent decades. However, a comprehensive understanding of its causes is not yet available. It is therefore essential to understand trends and mechanisms of allergy-inducing agents, such as fungal conidia. In this study, we investigated the hypothesis that environmental conditions linked to global atmospheric changes can affect the allergenicity of Aspergillus fumigatus, a common allergenic fungal species in indoor and outdoor environments and in airborne particulate matter. We show that fungi grown under present-day CO2 levels (392ppm) exhibit 8.5 and 3.5 fold higher allergenicity compared to fungi grown at preindustrial (280ppm) and double (560ppm) CO2 levels, respectively. A corresponding trend is observed in the expression of genes encoding for known allergenic proteins and in the major allergen Asp f1 concentrations, possibly due to physiological changes such as respiration rates and the nitrogen content of the fungus, influenced by the CO2 concentrations. Increased carbon and nitrogen levels in the growth medium also lead to a significant increase in the allergenicity. We propose that climatic changes such as increasing atmospheric CO2 levels and changes in the fungal growth medium may impact the ability of allergenic fungi such as A. fumigatus to induce allergies.

Aerosols influence the Earth's radiative budget by scattering and absorbing incoming solar radiation. The optical properties of aerosols vary as a function of wavelength, but few measurements have reported the wavelength dependence of aerosol extinction cross sections and complex refractive indices. We describe a new laboratory instrument to measure aerosol optical extinction as a function of wavelength, using cavity enhanced spectroscopy with a broadband light source. The instrument consists of two broadband channels which span the 360-390 and 385-420 nm spectral regions using two light emitting diodes (LED) and a grating spectrometer with charge-coupled device (CCD) detector. We determined aerosol extinction cross sections and directly observed Mie scattering resonances for aerosols that are purely scattering (polystyrene latex spheres and ammonium sulfate), slightly absorbing (Suwannee River fulvic acid), and strongly absorbing (nigrosin dye). We describe an approach for retrieving refractive indices as a function of wavelength from the measured extinction cross sections over the 360-420 nm wavelength region. The retrieved refractive indices for PSL and ammonium sulfate agree within uncertainty with the literature values for this spectral region. The refractive index determined for nigrosin is 1.78 (+/- 0.03) + 0.19 (+/- 0.08)i at 360 nm and 1.63 (+/- 0.03) + 0.21 (+/- 0.05)i at 420 nm. The refractive index determined for Suwannee River fulvic acid is 1.71 (+/- 0.02) + 0.07 (+/- 0.06)i at 360 nm and 1.66 (+/- 0.02) + 0.06 (+/- 0.04)i at 420 nm. These laboratory results support the potential for a field instrument capable of determining ambient aerosol optical extinction, average aerosol extinction cross section, and complex refractive index as a function of wavelength.

This study focuses on the heterogeneous reactions of gas phase glyoxal with aerosols of glycine, the most abundant amino acid in atmospheric aerosols, as well as with a mixture of glycine and ammonium sulfate (AS) at a molar ratio of 1:100 (glycine-AS 1:100). Aerosols were exposed to varying relative , humidity (RH) conditions in the presence of gas phase glyoxal for similar to 1 h, followed by drying and efflorescence. The changes in size, chemical composition, and optical properties were consequently measured. The reactions occur over a wide range of relative humidities, from similar to 30% up to 90% RH, covering values that are substantially lower as well as above the deliquescence point of the investigated aerosols. The product aerosols exhibit a trend of increasing growth in size, in optical extinction cross sections, and in extinction efficiencies (at lambda = 355 nm) with decreasing seed aerosol size, and with decreasing RH values from 90% to similar to 50%. For glycine-AS 1:100 particles, the ratio of the geometric cross section of the product aerosol to the original seed aerosol reached a value of similar to 3 the optical extinction cross section ratio was up to similar to 25, and the Q(ext) ratio was up to similar to 8, exceeding those of both AS and glycine separately, suggesting a synergistic effect. Aerosol mass spectrometer analyses show that the main products of all the studied reactions are glyoxal oligomers (light scattering compounds), with a minor contribution from imidazoles (absorbing compounds at lambda = 355 nm). These findings imply that the changes in the optical properties are likely due to enhanced scattering by the reaction products. The fraction of absorbing substances in the reacted aerosol increases with increasing RH, suggesting that the absorption component may become more substantial after longer reaction times, possibly in cloud or fog droplets. The results suggest that these reactions are possibly important in low RH regions, p

Credible climate change predictions require reliable fundamental scientific knowledge of the underlying processes. Despite extensive observational data accumulated to date, atmospheric aerosols still pose key uncertainties in the understanding of Earth's radiative balance due to direct interaction with radiation and because they modify clouds' properties. Specifically, major gaps exist in the understanding of the physicochemical pathways that lead to aerosol growth in the atmosphere and to changes in their properties while in the atmosphere. Traditionally, the driving forces for particle growth are attributed to condensation of low vapor pressure species following atmospheric oxidation of volatile compounds by gaseous oxidants. The current study presents experimental evidence of an unaccounted-for new photoinduced pathway for particle growth. We show that heterogeneous reactions activated by light can lead to fast uptake of noncondensable Volatile Organic Compounds (VOCs) at the surface of particles when only traces of a photosensitizer are present in the seed aerosol. Under such conditions, size and mass increase; changes in the chemical composition of the aerosol are also observed upon exposure to volatile organic compounds such as terpenes and near-UV irradiation. Experimentally determined growth rate values match field observations, suggesting that this photochemical process can provide a new, unaccounted-for pathway for atmospheric particle growth and should be considered by models.

Airborne fungal spores are an important fraction of atmospheric particulate matter and are major causative agents of allergenic and infectious diseases. Predicting the variability and species of allergy-causing fungal spores requires detailed and reliable methods for identification and quantification. There are diverse methods for their detection in the atmosphere and in the indoor environments; yet, it is important to optimize suitable methods for characterization of fungal spores in atmospheric samples. In this study we sampled and characterized total and specific airborne fungal spores from PM10 samples collected in Rehovot, Israel over an entire year. The total fungal spore concentrations vary throughout the year although the species variability was nearly the same. Seasonal equivalent spore concentrations analyzed by real-time quantitative-PCR-based methods were fall > winter > spring > summer. Reported concentrations based on ergosterol analysis for the same samples were and fall > spring > winter > summer. Correlation between the two analytical methods was found only for the spring season. These poor associations may be due to the per-spore ergosterol variations that arise from both varying production rates, as well as molecular degradation of ergosterol. While conversion of genome copies to spore concentration is not yet straightforward, the potential for improving this conversion and the ability of qPCR to identify groups of fungi or specific species makes this method preferable for environmental spore quantification. Identifying tools for establishing the relation between the presence of species and the actual ability to induce allergies is still needed in order to predict the effect on human health.

We report on a new ultrasensitive and fast technique for the detection and identification of both DNA and RNA with sensitivity of a few molecules. The new method is based on a patterned capillary tube (PCT) in which the internal surface of a glass tube is patterned with rings of different single-stranded DNA probes. A solution containing single-stranded analyte flows through the tube. Upon hybridization of appropriate DNA and RNA from the solution, DNA polymerase and reverse transcriptase (RT) are employed to synthesize the complementary nucleic acids with deoxynucleoside triphosphate (dNTP) labeled with fluorophores. The sample-analyte hybrids are detected by their fluorescence signal. We show that the new method is sensitive, is specific, can detect simultaneously both DNA and RNA from the same sample, and allows detection of analytes in serum.

Simultaneously retrieving the complex refractive indices of the core and shell of coated aerosol particles given the measured extinction efficiency as a function of particle dimensions (core diameter and coated diameter) is much more difficult than retrieving the complex refractive index of homogeneous aerosol particles. Not only must the minimization be performed over a four-parameter space, making it less efficient, but in addition the absolute value of the difference between the measured extinction and the calculated extinction does not have an easily distinguished global minimum. Rather, there are a number of local minima to which almost all conventional retrieval algorithms converge. In this work, we develop a new (to our knowledge) retrieval algorithm that employs the numerical method known as simulated annealing with an innovative "temperature" schedule. This study is limited only to spherical particles with a concentric shell and to cases in which the diameter of both the core and the coated particle are known. We find that when the top ranking particle sizes according to their information content are combined from separate experiments to make up the particle size distribution, the simulated annealing retrieval algorithm is quite robust and by far superior to a greedy random perturbation approach often used. (c) 2011 Optical Society of America

The heterogeneous reaction between gas phase glyoxal and ammonium sulfate (AS) aerosols, a proxy for inorganic atmospheric aerosol, was studied in terms of the dependence of the optical, physical and chemical properties of the product aerosols on initial particle size and ambient relative humidity (RH). Our experiments imitate an atmospheric scenario of a dry particle hydration at ambient RH conditions in the presence of glyoxal gas followed by efflorescence due to decrease of the ambient RH. The reactions were studied under different RH conditions, starting from dry conditions (similar to 20% RH) and up to 90% RH, covering conditions prevalent in many atmospheric environments, and followed by consequent drying of the reacted particles before their analysis by the aerosol mass spectrometer (AMS), cavity ring down (CRD) and scanning mobility particle sizer (SMPS) systems. At lambda = 355 nm, the reacted aerosols demonstrate a substantial growth in optical extinction cross section, as well as in mobility diameter under a broad range of RH values (35-90 %). The ratio of the product aerosol to seed aerosol geometric cross section reached up to similar to 3.5, and the optical extinction cross-section up to similar to 250. The reactions show a trend of increasing physical and optical growth with decreasing seed aerosol size, from 100 nm to 300 nm, as well as with decreasing RH values from 90% to similar to 40 %. Optically inactive aerosols, at the limit of the Mie range (100 nm diameter) become optically active as they grow due to the reaction. AMS analyses of the reaction of 300 nm AS at RH values of 50 %, 75% and 90% show that the main products of the reaction are glyoxal oligomers, formed by acetal formation in the presence of AS. In addition, imidazole formation, which is a minor channel, is observed for all reactions, yielding a product which absorbs at lambda = 290 nm, with possible implications on the radiative properties of the product aerosols. The ratio of ab

In-situ chemical composition measurements of ambient aerosols have been used for characterizing the evolution of submicron aerosols from a large anthropogenic biomass burning (BB) event in Israel. A high resolution Time of Flight Aerosol Mass Spectrometer (HR-RES-TOF-AMS) was used to follow the chemical evolution of BB aerosols during a night-long, extensive nationwide wood burning event and during the following day. While these types of extensive BB events are not common in this region, burning of agricultural waste is a common practice. The aging process of the BB aerosols was followed through their chemical, physical and optical properties. Mass spectrometric analysis of the aerosol organic component showed that aerosol aging is characterized by shifting from less oxidized fresh BB aerosols to more oxidized aerosols. Evidence for aerosol aging during the day following the BB event was indicated by an increase in the organic mass, its oxidation state, the total aerosol concentration, and a shift in the modal particle diameter. The effective broadband refractive index (EBRI) was derived using a white light optical particle counter (WELAS). The average EBRI for a mixed population of aerosols dominated by open fires was m = 1.53(+/- 0.03) + 0.07i(+/- 0.03), during the smoldering phase of the fires we found the EBRI to be m = 1.54(+/- 0.01) + 0.04i(+/- 0.01) compared to m = 1.49(+/- 0.01) + 0.02i(+/- 0.01) of the aged aerosols during the following day. This change indicates a decrease in the overall aerosol absorption and scattering. Elevated levels of particulate Polycyclic Aromatic Hydrocarbons (PAHs) were detected during the entire event, which suggest possible implications for human health during such extensive event.

This study focuses on the retrieval of the normalized mass absorption cross section ( MAC) of soot using theoretical calculations that incorporate new measurements of the optical properties of organic carbon (OC) intrinsic to fresh diesel soot. Intrinsic OC was extracted by water and an organic solvent, and the complex refractive index of the extracted OC was derived at 532 and 355-nm wavelengths using cavity ring-down aerosol spectrometry. The extracted OC was found to absorb weakly in the visible wavelengths and moderately at blue wavelengths. The mass ratio of OC and elemental carbon (EC) in the collected particles was evaluated using a thermo-optical method. The measured EC/OC ratio in the soot exhibited substantial variability from measurement to measurement, ranging between 2 and 5. To test the sensitivity of the MAC to this variability, three different EC/OC ratios (2:1, 1:1, and 1:2) were chosen as representative. Particle size and spherule morphology were estimated using scanning electron microscopy, and the soot was found to be primarily in the form of aggregates with a dominant aggregate diameter mode in the range 200-250 nm. The measured refractive index of the extracted OC was used with a variety of theoretical models to calculate the MAC of internally mixed diesel soot at 532 and 355 nm. We conclude that Rayleigh-Debye-Gans theory on clusters of coated spherules and T-matrix of a solid EC spheroid coated by intrinsic OC are both consistent with previous measurements; however, Rayleigh-Debye-Gans theory provides a more realistic physical model for the calculation

A workshop was held in the framework of the ACCENT (Atmospheric Composition Change - a European Network) Joint Research Programme on "Aerosols" and the Programme on "Access to Laboratory Data". The aim of the workshop was to hold "Gordon Conference" type discussion covering accommodation and reactive uptake of water vapour and trace pollutant gases on condensed phase atmospheric materials. The scope was to review and define the current state of knowledge of accommodation coefficients for water vapour on water droplet and ice surfaces, and uptake of trace gas species on a variety of different surfaces characteristic of the atmospheric condensed phase particulate matter and cloud droplets. Twenty-six scientists participated in this meeting through presentations, discussions and the development of a consensus review. In this review we present an analysis of the state of knowledge on the thermal and mass accommodation coefficient for water vapour on aqueous droplets and ice and a survey of current state-of the-art of reactive uptake of trace gases on a range of liquid and solid atmospheric droplets and particles. The review recommends consistent definitions of the various parameters that are needed for quantitative representation of the range of gas/condensed surface kinetic processes important for the atmosphere and identifies topics that require additional research.

P>Carbonyl sulfide (COS) exchange in C-3 leaves is linked to that of CO2, providing a basis for the use of COS as a powerful tracer of gross CO2 fluxes between plants and the atmosphere, a critical element in understanding the response of the land biosphere to global change. Here, we carried out controlled leaf-scale gas-exchange measurements of COS and CO2 in representative C-3 plants under a range of light intensities, relative humidities and temperatures, CO2 and COS concentrations, and following abscisic acid treatments. No 'respiration-like' emission of COS or detectable compensation point, and no cross-inhibition effects between COS and CO2 were observed. The mean ratio of COS to CO2 assimilation flux rates, As/Ac, was c. 1.4 pmol mu mol-1 and the leaf relative uptake (assimilation normalized to ambient concentrations, (As/Ac)(C(a)c/C(a)s)) was 1.6-1.7 across species and conditions, with significant deviations under certain conditions. Stomatal conductance was enhanced by increasing COS, which was possibly mediated by hydrogen sulfide (H2S) produced from COS hydrolysis, and a correlation was observed between As and leaf discrimination against C18OO. The results provide systematic and quantitative information necessary for the use of COS in photosynthesis and carbon-cycle research on the physiological to global scales.

Air quality transcends all scales with in the atmosphere from the local to the global with handovers and feedbacks at each scale interaction. Air quality has manifold effects on health, ecosystems heritage and, climate. In this review the state of scientific understanding in relation to global and regional air quality is outlined. The review discusses air quality, in terms of emissions, processing and transport of trace gases and aerosols. New insights into the characterization of both natural and anthropogenic emissions are reviewed looking at both natural (e.g. dust and lightning) as well as plant emissions. Trends in anthropogenic emissions both by region and globally are discussed as well as biomass burning emissions. In terms of chemical processing the major air quality elements of ozone, non-methane hydrocarbons, nitrogen oxides and aerosols are covered. A number of topics are presented as a way of integrating the process view into the atmospheric context; these include the atmospheric oxidation efficiency, halogen and HOx chemistry, nighttime chemistry, tropical chemistry, heat waves, megacities, biomass burning and the regional hot spot of the Mediterranean. New findings with respect to the transport of pollutants across the scales are discussed, in particular the move to quantify the impact of long-range transport on regional air quality. Gaps and research questions that remain intractable are identified. The review concludes with a focus of research and policy questions for the coming decade. In particular, the policy challenges for concerted air quality and climate change policy (co-benefit) are discussed. (C) 2009 Elsevier Ltd. All rights reserved.

By emission of volatile organic compounds (VOC) which
on oxidation form secondary organic aerosols (SOA) the
vegetation is coupled to atmosphere and climate. We
investigated new particle formation from tree emissions in a
new setup: a plant chamber housing the trees coupled to a
reaction chamber for oxidizing the plant emissions and for
forming SOA (J¸lich Plant Aerosol Atmosphere Chamber,
JPAC).
Boreal, temperate Midlatitude, and Mediterranean tree
species were studied and α-pinene was used as reference
compound to characterize the specifics of JPAC and to study
humidity and OH dependence of new particle formation. The
strength and the pattern of the tree emissions were varied by
increasing the temperature for the plants, thus mimicking the
higher frequency of occurrence of warmer days in a future
climate.
Under the experimental conditions OH radicals were
essential for inducing new particle formation, although O3 (≤
80 ppb) was always present and a part of the monoterpenes
and the sesquiterpenes reacted already with ozone before OH
was generated. Formation rates of 3 nm particles were linearly
related to the carbon mixing ratios of the VOC, as were the
maximum observed volume and the condensational growth
rates. The threshold of new particle formation was lower for
the tree emissions than for α-pinene.
Hygroscopic growth factors and activation to cloud
droplets were measured to characterize climate relevant
properties of the resulting aerosols. Overall the hygroscopic
properties of the biogenic SOA from the highly mixed tree
emissions are similar to those found for individual
monoterpenes and sesquiterpenes. However, changes of
emission pattern from species to species or induced by heat
stress is reflected in the hygroscopic properties of the resulting
SOA. The biogenic SOA revealed close to ideal Kˆhler
behavior with significantly reduced surface tension at
activation compared to pure water.

The major uncertainties associated with the direct impact of aerosols on climate call for fast and accurate characterization of their optical properties. Cavity ring down (CRD) spectroscopy provides highly sensitive measurement of aerosols' extinction coefficients from which the complex refractive index (RI) of the aerosol may be retrieved accurately for spherical particles of known size and number density, thus it is possible to calculate the single scattering albedo and other atmospherically relevant optical parameters. We present a CRD system employing continuous wave (CW) single mode laser. The single mode laser and the high repetition rate obtained significantly improve the sensitivity and reliability of the system, compared to a pulsed laser CRD setup. The detection limit of the CW-CRD system is between 6.67 x 10(-10) cm(-1) for an empty cavity and 3.63 x 10(-9) cm(-1) for 1000 particles per cm(3) inside the cavity, at a 400 Hz sampling and averaging of 2000 shots for one sample measurement taken in 5 s. For typical pulsed-CRD, the detection limit for an empty cavity is less than 3.8 x 10(-1) cm(-1) for 1000 shots averaged over 100 s at 10 Hz. The system was tested for stability, accuracy, and RI retrievals for scattering and absorbing laboratory-generated aerosols. Specifically, the retrieved extinction remains very stable for long measurement times (1 h) with an order of magnitude change in aerosol number concentration. In addition, the optical cross section (sigma(ext)) of a 400 nm polystyrene latex sphere (PSL) was determined within 2% error compared to the calculated value based on Mie theory. The complex RI of PSL, nigrosin, and ammonium sulfate (AS) aerosols were determined by measuring the extinction efficiency (Q(ext)) as a function of the size parameter ((pi D)/lambda) and found to be in very good agreement with literature values. A mismatch in the retrieved RI of Suwannee River fulvic acid (SRFA) compared to a previous study was observed and is a

Emission of biogenic volatile organic compounds (VOC) which on oxidation form secondary organic aerosols (SOA) can couple the vegetation with the atmosphere and climate. Particle formation from tree emissions was investigated in a new setup: a plant chamber coupled to a reaction chamber for oxidizing the plant emissions and for forming SOA. Emissions from the boreal tree species birch, pine, and spruce were studied. In addition, alpha-pinene was used as reference compound. Under the employed experimental conditions, OH radicals were essential for inducing new particle formation, although O-3 (

Humic-like substances (HULIS) in the atmosphere are ubiquitous macromolecular substances that comprise a major fraction of the organic component of atmospheric aerosols. In this study we report that HULIS extracted from collected wood burning and urban pollution atmospheric particles enhance aqueous phase oxidation of model organic contaminants (pyrene and phenol), by promoting the dark Fenton reaction under atmospherically relevant conditions. The paucity of radical sources at night makes this reaction, which is not accounted for in cloud chemistry models, potentially quite important for understanding and quantifying in-cloud degradation of organic pollutants, and for understanding Fe oxidation state speciation in atmospheric waters. Citation: Moonshine, M., Y. Rudich, S. Katsman, and E. R. Graber (2008), Atmospheric HULIS enhance pollutant degradation by promoting the dark Fenton reaction, Geophys. Res. Lett., 35, L20807, doi: 10.1029/2008GL035285.

Observations indicate that the amount of solar radiation reaching the surface of the Earth has varied significantly over decadal timescales during the past half century. A workshop of the Israel Science Foundation evaluated the observational evidence for global dimming and brightening (GDB), its possible causes, and its implications for the Earth’s climate, hydrology, agriculture, and land use. The workshop also identified gaps in our knowledge and made recommendations to fill these gaps. Speakers at the workshop reviewed current understanding of GDB. Surface observations indicate that widespread global dimming (reduced solar radiation) at a rate of about 2–3 watts per square meter per decade occurred between the late 1950s and the late 1980s over mid-latitude land surfaces of the Northern Hemisphere. These records also show a reversal of this trend over many land areas in the past two decades—brightening of the order of 2 watts per square meter per decade. Satellite estimates of solar radiation reaching the surface and aerosol trends, only available since the early 1980s, are generally consistent with these findings. Some analyses of the surface observations indicate that the rates of dimming and brightening are highest in major population centers and fall off significantly in areas with lower population densities....

In this study, we measure the extinction efficiency at 532 nm of absorbing aerosol particles coated with a non-absorbing solid and liquid organic shell with coating thickness varying between 5 and 100 nm using cavity ring down aerosol spectrometry. For this purpose, we use nigrosin, an organic black dye, as a model absorbing core and two non-absorbing organic substances as shells, glutaric acid (GA) and Di-Ethyl-Hexyl-Sebacate (DEHS). The measured behavior of the coated particles is consistent with Mie calculations of core-shell particles. Errors between measured and calculated values for nigrosin coated with GA and DEHS are between 0.5% and 10.5% and between 0.5% and 9%, respectively. However, it is evident that the calculations are in better agreement with the measured results for thinner coatings. Possible reasons for these discrepancies are discussed.

Surface-active organics such as humic-like substances (HULIS) are abundant in aerosol particles and can lower the surface tension of cloud droplets forming on secondary organic and biomass burning aerosols. How fast is the diffusion of these species, relative to the time scale of cloud droplet growth? Here we report surface tension measurements of solutions containing HULIS extracted from smoke and pollution aerosol particles as well those of molecular weight-fractionated aquatic fulvic acids. Diffusion coefficients are estimated based on the Gibbs adsorption isotherms. The results suggest that HULIS diffusion to the surface of forming droplets is typically more rapid than the time scale of droplet growth so that cloud microphysical properties are affected.

The hygroscopic growth (HG) of humic-like substances (HULIS) extracted from smoke and pollution aerosol particles and of Suwannee River fulvic acid (SRFA, bulk and fractions of different molecular weight) was measured by humidity tandem differential mobility analyzer (H-TDMA). By characterizing physical and chemical parameters such as molecular weight, elemental composition, and surface tension, we test the effect of these parameters on particle interactions with water vapor. For molecular weight-fractionated SRFA fractions, the growth factor at 90% relative humidity was generally inversely proportional to the molecular weight. HULIS extracts from ambient particles are more hygroscopic than all the SRFA fractions and exhibit different hygroscopic properties depending on their origin and residence time in the atmosphere. The results point out some dissimilarities between SRFA and aerosol- derived HULIS. The cloud condensation nuclei (CCN) behavior of the studied materials was predicted on the basis of hygroscopic growth using a recently introduced approach of Kreidenweis et al. (2005) and compared to CCN activity measurements on the same samples (Dinar et al., 2006). It is found that the computational approach (Kreidenweis et al., 2005) works reasonably well for SRFA fractions but is limited in use for the HULIS extracts from aerosol particles. The difficulties arise from uncertainties associated with HG measurements at high relative humidity, which leads to large errors in the predicted CCN activity.

Application of cavity ring down (CRD) spectrometry for measuring the optical properties of pure and mixed laboratory-generated aerosols is presented. The extinction coefficient (alpha(ext)), extinction cross section (sigma(ext)) and extinction efficiency (Q(ext)) were measured for polystyrene spheres (PSS), ammonium sulphate ((NH4)(2)(SO4)), sodium chloride (NaCl), glutaric acid (GA), and Rhodamine-590 aerosols. The refractive indices of the different aerosols were retrieved by comparing the measured extinction efficiency of each aerosol type to the extinction predicted by Mie theory. Aerosols composed of sodium chloride and glutaric acid in different mixing ratios were used as model for mixed aerosols of two non-absorbing materials, and their extinction and complex refractive index were derived. Aerosols composed of Rhodamine-590 and ammonium sulphate in different mixing ratios were used as model for mixing of absorbing and non-absorbing species, and their optical properties were derived. The refractive indices of the mixed aerosols were also calculated by various optical mixing rules. We found that for non-absorbing mixtures, the linear rule, Maxwell-Garnett rule, and extended effective medium approximation (EEMA), give comparable results, with the linear mixing rule giving a slightly better fit than the others. Overall, calculations for the mixed aerosols are not as good as for single component aerosols. For absorbing mixtures, the differences between the refractive indices calculated using the mixing rules and those retrieved by CRD are generally higher.

The aerosol characterization experiment performed within the Large-Scale Biosphere-Atmosphere Experiment in Amazonia-Smoke, Aerosols, Clouds, Rainfall and Climate (LBA-SMOCC) field experiment carried out in Rondonia, Brazil, in the period from September to November 2002 provides a unique data set of size-resolved chemical composition of boundary layer aerosol over the Amazon Basin from the intense biomass-burning period to the onset of the wet season. Three main periods were clearly distinguished on the basis of the PM10 concentration trend during the experiment: (1) dry period, with average PM10 well above 50 mu g m(-3); (2) transition period, during which the 24-hour-averaged PM10 never exceeded 40 mu g m(-3) and never dropped below 10 mg m(-3); (3) and wet period, characterized by 48-hour-averaged concentrations of PM10 below 12 mu g m(-3) and sometimes as low as 2 mu g m(-3). The trend of PM10 reflects that of CO concentration and can be directly linked to the decreasing intensity of the biomass- burning activities from September through November, because of the progressive onset of the wet season. Two prominent aerosol modes, in the submicron and supermicron size ranges, were detected throughout the experiment. Dry period size distributions are dominated by the fine mode, while the fine and coarse modes show almost the same concentrations during the wet period. The supermicron fraction of the aerosol is composed mainly of primary particles of crustal or biological origin, whereas submicron particles are produced in high concentrations only during the biomass-burning periods and are mainly composed of organic material, mostly water-soluble, and similar to 10% of soluble inorganic salts, with sulphate as the major anion. Size-resolved average aerosol chemical compositions are reported for the dry, transition, and wet periods. However, significant variations in the aerosol composition and concentrations were observed within each period, which can be classif

About 40 million tons of dust are transported annually from the Sahara to the Amazon basin. Saharan dust has been proposed to be the main mineral source that fertilizes the Amazon basin, generating a dependence of the health and productivity of the rain forest on dust supply from the Sahara. Here we show that about half of the annual dust supply to the Amazon basin is emitted from a single source: the Bodele depression located northeast of Lake Chad, approximately 0.5% of the size of the Amazon or 0.2% of the Sahara. Placed in a narrow path between two mountain chains that direct and accelerate the surface winds over the depression, the Bodele emits dust on 40% of the winter days, averaging more than 0.7 million tons of dust per day.

The transport of anthropogenic pollution by desert dust in the Eastern Mediterranean region was studied by analyzing major and trace element composition, organic species, and Pb isotope ratios in suspended dust samples collected in Jerusalem, Israel. Dust storms in this region are associated with four distinct synoptic conditions (Red Sea Trough (RS), Eastern High (EH), Sharav Cyclone (SC), and Cold Depression (Cyprus low, CD)) that carry dust mostly from North African (SC, CD, EH) and Arabian and Syrian (RS, EH) deserts. Substantial contamination of dust particles by Pb, Cu, Zn, and Ni is observed, while other elements (Na, Ca, Mg, Mn, Sr, Rb, REE, U, and Th) display natural concentrations. Sequential extraction of the abovementioned elements from the dust samples shows that the carbonate and sorbed fractions contain most of the pollution, yet the Al-silicate fraction is also contaminated, implying that soils and sediments in the source terrains of the dust are already polluted. We identified the pollutant sources by using Pb isotopes. It appears that before the beginning of the dust storm, the pollutants in the collected samples are dominated by local sources but with the arrival of dust from North Africa, the proportion of foreign pollutants increases. Organic pollutants exhibit behavior similar and complementary to that of the inorganic tracers, attesting to the importance of anthropogenic-pollutant addition en route of the dust from its remote sources. Pollution of suspended dust is observed under all synoptic conditions, yet it appears that easterly winds carry higher proportions of local pollution and westerly winds carry pollution emitted in the Cairo basin. Therefore, pollution transport by mineral dust should be accounted for in environmental models and in assessing the health-related effects of mineral dust.

A class of organic molecules extracted from atmospheric aerosol particles and isolated from fog and cloud water has been termed HUmic-LIke Substances (HULIS) due to a certain resemblance to terrestrial and aquatic humic and fulvic acids. In light of the interest that this class of atmospheric compounds currently attracts, we comprehensively review HULIS properties, as well as laboratory and field investigations concerning their formation and characterization in atmospheric samples. While sharing some important features such as polyacidic nature, accumulating evidence suggests that atmospheric HULIS differ substantially from terrestrial and aquatic humic substances. Major differences between HULIS and humic substances, including smaller average molecular weight, lower aromatic moiety content, greater surface activity, better droplet activation ability, as well as others, are highlighted. Several alternatives are proposed that may explain such differences: (1) the possibility that mono- and di-carboxylic acids and mineral acids abundant in the atmosphere prevent the formation of large humic "supramolecular associations"; (2) that large humic macromolecules are destroyed in the atmosphere by UV radiation, O-3, and OH- radicals; 3) that "HULIS" actually consists of a complex, unresolved mixture of relatively small molecules rather than macromolecular entities; and (4) that HULIS formed via abiotic and short-lived oxidative reaction pathways differ substantially from humic substances formed over long time periods via biologically-mediated reactions. It should also be recalled that the vast majority of studies of HULIS relate to the water soluble fraction, which would include only the fulvic acid fraction of humic substances, and exclude the humic acid (base-soluble) and humin (insoluble) fractions of humic substances. A significant effort towards adopting standard extraction and characterization methods is required to develop a better and meaningful comparison between

Clouds developing in a polluted environment tend to have more numerous but smaller droplets. This property may lead to suppression of precipitation and longer cloud lifetime. Absorption of incoming solar radiation by aerosols, however, can reduce the cloud cover. The net aerosol effect on clouds is currently the largest uncertainty in evaluating climate forcing. Using large statistics of 1-km resolution MODIS (Moderate Resolution Imaging Spectro-radiometer) satellite data, we study the aerosol effect on shallow water clouds, separately in four regions of the Atlantic Ocean, for June through August 2002: marine aerosol (30 degrees S-20 degrees S), smoke (20 degrees S-5 degrees N), mineral dust (5 degrees N-25 degrees N), and pollution aerosols (30 degrees N160 degrees N). All four aerosol types affect the cloud droplet size. We also find that the coverage of shallow clouds increases in all of the cases by 0.2-0.4 from clean to polluted, smoky, or dusty conditions. Covariability analysis with meteorological parameters associates most of this change to aerosol, for each of the four regions and 3 months studied. In our opinion, there is low probability that the net aerosol effect can be explained by coincidental, unresolved, changes in meteorological conditions that also accumulate aerosol, or errors in the data, although further in situ measurements and model developments are needed to fully understand the processes. The radiative effect at the top of the atmosphere incurred by the aerosol effect on the shallow clouds and solar radiation is -11 +/- 3 W/m(2) for the 3 months studied; 2/3 of it is due to the aerosol-induced cloud changes, and 1/3 is due to aerosol direct radiative effect.

Prior to the massive use of new oxygenated solvents, data on their multiphase reactivity must be obtained to assess their environmental fate and impact on water and air quality. For this, the kinetics and mechanisms of the photochemical and photocatalytic degradation of selected oxygenated solvents by common tropospheric oxidants (such as OH and ozone) must be characterized. We studied the oxidation kinetics of new oxygenated solvents as pure organic liquids and in an aqueous medium by ozone and by the OH radical, respectively. The studied chemicals are all unsaturated compounds, having none, one, or two ether groups. The results indicate that the OH reaction proceeds at the diffusion limit by addition to the double bond. The reactive uptake coefficients associated with the reaction initiated by ozone are of the order of 10(-3). The reactions of compounds with two double bonds are very fast and probably occur at the surface. This kinetic information demonstrates that organic solvents in an organic medium or in an aqueous droplet will be oxidized rapidly by these oxidation reactions. These reactions, however, are not significant sinks for ozone and OH radicals.

Biomass burning is an important source of smoke aerosol particles, which contain water-soluble inorganic and organic species, and thus have a great potential of affecting cloud formation, precipitation, and climate on global and regional scales. In this study, we have developed a new chromatographic method for the determination of levoglucosan (a specific tracer for biomass burning particles), related polyhydroxy compounds, and 2-methylerythritol (recently identified as isoprene oxidation product in fine aerosols in the Amazon) in smoke and in rainwater samples. The new method is based on water extraction and utilizes ion-exclusion high-performance liquid chromatography (IEC-HPLC) separation and spectroscopic detection at 194 nm. The new method allows the analysis of wet samples, such as rainwater samples. In addition, aliquots of the same extracts can be used for further analyses, such as ion chromatography. The overall method uncertainty for sample analysis is 15%. The method was applied to the analysis of high-volume and size-segregated smoke samples and to rainwater samples, all collected during and following the deforestation fires season in Rondonia, Brazil. From the analysis of size-segregated samples, it is evident that levoglucosan is a primary vegetation combustion product, emitted mostly in the 0.175-1 mu m size bins. Levoglucosan concentrations decrease below the detection limit at the end of the deforestation fires period, implying that it is not present in significant amounts in background Amazon forest aerosols. The ratio of daytime levoglucosan concentration to particulate matter (PM) concentration was about half the nighttime ratio. This observation is rationalized by the prevalence of flaming combustion during day as opposed to smoldering combustion during night. This work broadens the speciation possibilities offered by simple HPLC and demonstrates the importance of multianalysis of several kinds of samples for a deeper understanding of biomass

This paper introduces the capability to study simultaneously changes in the density, the chemical composition, the mobility diameter, the aerodynamic diameter, and the layer thickness of multi-layered aerosol particles as they are being altered by heterogeneous chemical reactions. A vaporization-condensation method is used to generate aerosol particles composed of oleic acid outer layers of 2 to 30 nm on 101-nm polystyrene latex cores. The layer density is modified by reaction of oleic acid with ozone for variable exposure times. For increasing ozone exposure, the mobility diameter decreases while the vacuum aerodynamic diameter increases, which, for spherical particles, implies that particle density increases. The aerosol particles are confirmed as spherical based upon the small divergence of the particle beam in the aerosol mass spectrometer. The particle and layer densities are calculated by two independent methods, namely one based on the measured aerodynamic and mobility diameters and the other based on the measured mobility diameter and particle mass. The uncertainty estimates for density calculated by the second method are two to three times greater than those of the first method. Both methods indicate that the layer density increases from 0.89 to 1.12 g(.)cm(-3) with increasing ozone exposure. Aerosol mass spectrometry shows that, concomitant with the increase in the layer density, the oxygen content of the reacted layer increases. Even after all of the oleic acid has reacted, the layer density and the oxygen content continue to increase slowly with prolonged ozone exposure, a finding which indicates continued chemical reactions of the organic products either with ozone or with themselves. The results of this paper provide new insights into the complex changes occurring for atmospheric particles during the aging processes caused by gas-phase oxidants.

Changes in aerosol composition associated with a cold front passage were examined during a field experiment in Tel Aviv, Israel (2-15 Dec, 2000). In addition to monitoring aerosol scattering and optical thickness, aerosol samples were collected for detailed chemical analyses. Data were compared to simultaneous measurements made at Sde Boker, a semi-remote site in the Negev Desert, to help determine what changes were due to local pollution as opposed to regional phenomena. During the pre-frontal period (2-7 Dec) both sites were influenced by air masses containing a relatively high content of sulphate and dust, originating from neighbouring regions of the Middle East. A steady build-up of local pollution was then observed in Tel Aviv due to vehicular emissions/industrial activities, as indicated by increasing concentrations of black carbon, organic carbon, V, Cu, Ni, Zn, Br, Pb, NO3- and PAHs. Identification of a number of organic biomass burning tracers (e.g., levoglucosan) indicates that smoke also contributed to the pollution build-up in Tel Aviv, while a range of sugars/sugar alcohols point to a microbial/bioaerosol component. Locally emitted pollutants tended to exhibit higher nighttime concentrations due to trapping of pollution under a nocturnal inversion. Fine aerosol iodine was the only element exhibiting higher daytime concentrations, hinting at a photochemical source. Post-frontal measurements (12-15 Dec) revealed a significant decrease in all pollutants due to dispersal of the haze by the cold front 66 (8-9 Dec), with the air initially being dominated by marine aerosol. Concentrations of pollutants then began to increase, with backward trajectories indicating a possible contribution from Eastern Europe. Overall, the study identified a range of useful tracers for monitoring the contribution of different sources to the aerosol over Israel. Crown Copyright (C) 2003 Published by Elsevier Ltd. All rights reserved.

[1] We investigated nucleation scavenging of aerosols by cloud drops during the passage of a shallow cold front at a mountain station in northern Israel. The chemical composition and size of the aerosols were measured during and following the passage of the front. Analysis of the air mass trajectories show that, prior to the frontal passage, the air originated from the north, bringing with it pollution particles from sources in Eastern Europe. Following the frontal passage, the air originated from the east, bringing with it some mineral dust particles. The results show that sulfate, nitrate, and ammonium were the dominant compounds in the particles. Of the total sulfate-containing particles, 65% nucleated cloud drops. We found nucleation scavenging of aerosols to be correlated with the size of the aerosols. Aerosols smaller than 0.14 mum were not significantly affected by nucleation scavenging, while the number concentration of particles larger than 0.14 mm decreased in correspondence to the increase in droplet concentrations. During the time that the cloud covered the measuring site, 80% of the particles in the size range 0.3-1 mum were scavenged. The concentrations of the particles with diameter smaller than 1 mm returned to their original values after the cloud dissipated.

Rate coefficients for the reaction of OH radical with eleven C-3-C-6 hydroxyalkyl nitrates and with two C-4 hydroxy nitrates containing a double bond were determined at atmospheric pressure and 296 +/- 2 K. The rate coefficients were measured in a photochemical reactor by the relative rate technique, employing solid-phase microextraction (SPME) coupled to gas chromatography (GC) for detection of the organic reactants. Hydroxyalkyl nitrates react faster than alkyl nitrates with the OH radical. The rate coefficients increase with increasing chain length and separation between the hydroxy and the nitrooxy groups. By including different loss processes such as photolysis, gas-phase reactions, and solubility, the tropospheric lifetime of C-3-C-6 hydroxyalkyl nitrates is estimated to range between 0.5 and 4.5 days. Due to their higher reactivity and solubility, hydroxyalkyl nitrates have a shorter atmospheric lifetime than alkyl nitrates.

Applications of new retrieval methods to old satellite data allowed us to study the effects of smoke from the Kuwait oil fires in 1991 on clouds and precipitation. The properties of smoke-affected and smoke-free clouds were compared on the background of the dust-laden desert atmosphere. Several effects were observed: (1) clouds typically developed at the top of the smoke plume, probably because of solar heating and induced convection by the strongly absorbing aerosols; (2) large salt particles from the burning mix of oil and brines formed giant cloud condensation nuclei (CCN) close to the source, which initiated coalescence in the highly polluted clouds; (3) farther away from the smoke source, the giant CCN were deposited, and the extremely high concentrations of medium and small CCN dominated cloud development by strongly suppressing drop coalescence and growth with altitude; and (4) the smaller cloud droplets in the smoke-affected clouds froze at colder temperatures and suppressed both the water and ice precipitation forming processes. These observations imply that over land the smoke particles are not washed out efficiently and can be transported to long distances, extending the observed effects to large areas. The absorption of solar radiation by the smoke induces convection above the smoke plumes and consequently leads to formation of clouds with roots at the top of the smoke layer. This process dominates over the semidirect effect of cloud evaporation due to the smoke-induced enhanced solar heating, at least in the case of the Kuwait fires.

[1] High concentrations of small atmospheric aerosols are known to reduce the size of cloud droplets, increase cloud albedo and suppress precipitation formation. In contrast, cloud simulations suggest that even low concentrations of large soluble aerosols should promote droplets' growth and rainfall. Until now, though, no observational evidence of such microphysical effects in natural circumstance over land has been presented. By using NOAA-AVHRR retrievals on cases where salt-dust from the Aral Sea interacts with clouds we show that large salt-containing dust particles increase cloud drops to sizes that promote precipitation. These findings are in line with the findings of the microphysical models and recent results from hygroscopic cloud seeding experiments for rain enhancement.

Rate coefficients for the gas-phase reactions of chlorine atoms with a series of C-3-C-6 hydroxyalkyl nitrates of atmospheric interest have been determined at 296 +/- 2 K and atmospheric pressure. The experiments were conducted using the relative rate technique combined with solid-phase microextraction (SPME) sampling followed by gas chromatography (GC) analysis with an electron capture detector (ECD). The experiments were performed in a collapsible 100 L PVF-film (Tedlar) reaction chamber. It is shown that the presence of the hydroxy group enhances the reactivity of the hydroxyalkyl nitrates toward the Cl atom as compared to the corresponding alkyl nitrates and alkyl dinitrates. The Cl atom reactivity toward the hydroxyalkyl nitrates increases with the length of the alkyl chain and with increasing separation between the hydroxy and the nitrooxy groups. Tropospheric lifetimes are calculated using the determined rate coefficients and the atmospheric implications are briefly discussed.

Multifunctional organic compounds are thought to constitute a major component of the organic matter found in atmospheric particles. Their partitioning into the organic matter depends on their structure, their chemical properties and the properties of the absorbing matrix. It was recently shown that octanol is a suitable surrogate for organic particles and the octanol-air partition coefficient (K-OA) was suggested as a useful tool for estimating the partitioning of organic compounds into atmospheric particles that contain high organic mass fractions. In this paper, we present a new and simple technique for the determination of KOA using solid phase microextraction (SPME) relative to a known Henry's law constant. We apply the technique for the determination of K-OA of beta-, gamma- and delta -C-3-C-5 hydroxy alkyl nitrates. The temperature dependence of K-OA for some of the compounds is also measured. It is shown that the solubility constants of these compounds are higher in octanol than in water and that the solubility in octanol increases with the length of the hydrophobic chain and with increasing distance between the hydroxy and the nitrooxy groups. Partition coefficients between the gas and particulate phase (K-p) are calculated using the determined K-OA values and their atmospheric implications are discussed. (C) 2001 Elsevier Science Ltd, All rights reserved.

Using a new type of ion trap, we demonstrate that the length of a packet of charged particles oscillating between two electrostatic mirrors will remain constant under special conditions. The effect can be understood in terms of phase synchronization, where, in a rather counter-intuitive way, the repulsive Coulomb interaction between the ions actually holds the packet together. Application of this effect for mass spectrometry is discussed.

The effect of desert dust on cloud properties and precipitation has so far been studied solely by using theoretical models, which predict that rainfall would be enhanced. Here we present observations showing the contrary; the effect of dust on cloud properties is to inhibit precipitation. Using satellite and aircraft observations we show that clouds forming within desert dust contain small droplets and produce little precipitation by drop coalescence. Measurement of the size distribution and the chemical analysis of individual saharan dust particles collected in such a dust storm suggest a possible mechanism for the diminished rainfall. The detrimental impact of dust on rainfall is smaller than that caused by smoke from biomass burning or anthropogenic air pollution, but the large abundance of desert dust in the atmosphere renders it important. The reduction of precipitation from clouds affected by desert dust can cause drier soil, which in turn raises more dust, thus providing a possible feedback loop to further decrease precipitation. Furthermore, anthropogenic changes of land use exposing the topsoil can initiate such a desertification feedback process.

The interaction between water and organic substances is of extreme importance in physical, biological, and geological chemistries. Understanding the interactions between water and organic interfaces is one of the earliest chemical quandaries. In this research, self-assembled monolayers (SAMs) were used as a tool to investigate the interaction between water molecules and hydrophobic surfaces. Real-time adsorption and desorption kinetics of water on hydrophobic SAM surfaces was monitored using a new type of field effect transistor (FET)-like device called MOCSER (molecular controlled semiconductor resistor) coated with SAMs, A quartz crystal microbalance (QCM) was used as a complementary technique to give an estimate of total water mass adsorbed. It is shown that water adsorption depends on relative humidity and is reversible. The amount of adsorbed water increased with surface corrugation. The measurements suggest that adsorption takes place as small water clusters, originating on irregularities on the surface organic layer. Molecular dynamics simulations were carried out to study the interactions of water and hydrophobic surfaces as well. These simulations also suggest the formation of water microdroplets on hydrophobic surfaces, and indicate a strong correlation between increased surface corrugation and adsorption. This paper examines the possible consequences of these interactions on the properties of organic aerosols in the troposphere.

The OH- and O-3-initiated oxidation of five monoterpenes (myrcene, terpinolene, Delta(3)-carene, alpha-pinene, and beta-pinene) has been studied in environmental chambers equipped with either a Fourier transform infrared spectrometer or a gas chromatography/flame ionization detector system. The OH-oxidation of myrcene and terpinolene is shown to lead to substantial yields of acetone (36 and 39%, respectively), while the acetone yield from the pinene compounds is quite small (4% and similar to 2%, for alpha- and beta-pinene, respectively). Formaldehyde has been identified as a major product (yields of 20-40%) in the OH-initiated oxidation of all five species. Formic acid was also observed in the OH-initiated oxidation of all five monoterpenes, with yields of 2% from beta-pinene and 5-9% from the other species studied. The production of acetone from the reaction of monoterpenes with ozone in the presence of an OH scavenger was measured. The yields of acetone for the O-3 reactions were alpha-pinene, 0.03 +/- 0.01; beta-pinene, 0.009 + 0.009; Delta(3)-carene, 0.10 +/- 0.015; myrcene, 0.25 +/- 0.06; and terpinolene, 0.50 + 0.06. The mechanism leading to the production of these compounds is discussed, as is the atmospheric relevance of the results. In particular, an estimate of the contribution of monoterpene oxidation to observed atmospheric levels of acetone and formic acid is made.

The rate coefficient of the CH3C(O)O-2 + NO gas-phase reaction was measured over the temperature range of 218-370 K and total pressure of 2-5 Ton, using chemical ionization mass spectrometry detection of the CH3C(O)O-2 radical. The temperature-dependent expression for the rate coefficient was determined to be k(T) = (6.0 +/- 1.1) x 10(-12) exp{(320 +/- 40)/T} cm(3) molecule(-1) s(-1), and a 298 K rate constant k(298) = (1.8 +/- 0.3) x 10(-11) cm(3) molecule(-1) s(-1) was found. These results quell some of the ambiguity presented by previous studies of this reaction and validate the recommended value to be used in tropospheric chemistry models.

The rate coefficients for the reactions of O(3P) with CF3I (1) and CH3I (2) were measured between 213 and 364 K to be: k1(T) ) (7.9 ( 0.8) x 10-12 exp[-(175 ( 40)/T] and k2(T) ) (1.0 ( 0.2) x 10-11 exp[(160 (50)/T] cm3 molecule-1 s-1. The rate coefficients for the reaction of O(3P) with CD3I, (CH3)2CHCH2I, (CH3)2-CHI, CF3CH2I, CF3CHFI, and CF3CF2I at 298 K were also measured. The yields of the IO and CF3O products in reaction 1 at 298 K were found to be 0.83 ( 0.09 and

Keywords: Chemistry, Physical; Optics; Physics, Atomic, Molecular & Chemical; Spectroscopy

Reactions of O(1D) with hydrocarbon monomers and clusters were investigated via a cross molecular beam experiment applying laser induced fluorescence for the detection of the OH product. The translational, vibrational, rotational, spin-orbit, and A-doubling state populations were analyzed. Based on this information the mechanisms for the reactions of O(1D) with methane, propane, and their clusters were established. Nonstatistical distributions are observed even for the reaction of large clusters and are discussed in terms of nonadiabatic effects induced by the long lived collision complex.