Publications

Ice-binding proteins (IBPs) are found in many organisms, such as fish and hexapods, plants, and bacteria that need to cope with low temperatures. Ice nucleation and thermal hysteresis are two attributes of IBPs. While ice nucleation is promoted by large proteins, known as ice nucleating proteins, the smaller IBPs, referred to as antifreeze proteins (AFPs), inhibit the growth of ice crystals by up to several degrees below the melting point, resulting in a thermal hysteresis (TH) gap between melting and ice growth. Recently, we showed that the nucleation capacity of two types of IBPs corresponds to their size, in agreement with classical nucleation theory. Here, we expand this finding to additional IBPs that we isolated from snow fleas (the arthropod Collembola), collected in northern Israel. Chemical analyses using circular dichroism and Fourier-transform infrared spectroscopy data suggest that these IBPs have a similar structure to a previously reported snow flea antifreeze protein. Further experiments reveal that the ice-shell purified proteins have hyperactive antifreeze properties, as determined by nanoliter osmometry, and also exhibit low ice-nucleation activity in accordance with their size.

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-1 beta and tumor necrosis factor (TNF)-alpha were with most species. Most species were related to IL-1 beta, 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-alpha was associated with primary sources, whereas IL-1 beta 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.

Nrf2 is an important transcription factor implicated in the oxidative stress response, which has been reported to play an important role in the way by which air pollution particulate matter (PM2.5) induces adverse health effects. This study investigates the mechanism by which Nrf2 exerts its protective effect in PM2.5 induced toxicity in lung cells. Lung cells silenced for Nrf2 (shNrf2) demonstrated diverse susceptibility to various PM extracts; water extracts containing high levels of dissolved metals exhibited higher capacity to generate mitochondrial reactive oxygen species (ROS) and hence increased oxidative stress levels. Organic extracts containing high levels of polycyclic aromatic hydrocarbons (PAHs) increased mortality and reduced ROS production in the silenced cells. shNrf2 cells exhibited a higher basal mitochondrial respiration rate compared to the control cells. Following exposure to water extracts, the mitochondrial respiration increased, which was not observed with the organic extracts. shNrf2 cells exposed to the organic extracts showed lower mitochondrial membrane potential and lower mtDNA copy number. Nrf2 may act as a signaling mediator for the mitochondria function following PM2.5 exposure. 

We present the laboratory results of immersion freezing efficiencies of cellulose particles at supercooled temperature (T) conditions. Three types of chemically homogeneous cellulose samples are used as surrogates that represent supermicron and submicron ice-nucleating plant structural polymers. These samples include microcrystalline cellulose (MCC), fibrous cellulose (FC) and nanocrystalline cellulose (NCC). Our immersion freezing dataset includes data from various ice nucleation measurement techniques available at 17 different institutions, including nine dry dispersion and 11 aqueous suspension techniques. With a total of 20 methods, we performed systematic accuracy and precision analysis of measurements from all 20 measurement techniques by evaluating T-binned (1 ∘C) data over a wide T range (−36 ∘C <T<−4 ∘C). Specifically, we intercompared the geometric surface area-based ice nucleation active surface site (INAS) density data derived from our measurements as a function of T, ns,geo(T). Additionally, we also compared the ns,geo(T) values and the freezing spectral slope parameter (Δlog(ns,geo)/ΔT)from our measurements to previous literature results. Results show all three cellulose materials are reasonably ice active. The freezing efficiencies of NCC samples agree reasonably well, whereas the diversity for the other two samples spans ≈ 10 ∘C. Despite given uncertainties within each instrument technique, the overall trend of the ns,geo(T) spectrum traced by the T-binned average of measurements suggests that predominantly supermicron-sized cellulose particles (MCC and FC) generally act as more efficient ice-nucleating particles (INPs) than NCC with about 1 order of magnitude higher ns,geo(T).

It has been hypothesized that the cytotoxicity of secondary organic aerosols (SOA) is mediated through the formation of reactive oxygen species (ROS) in the exposed cells. Here, lung epithelial cells (A549) residing at the air-liquid interface were exposed to proxies of anthropogenic and biogenic SOA that were photochemically aged under varying nitrogen oxide (NOx) concentrations in an oxidation flow reactor. The total organic peroxides and ROS radical content in the SOA were quantified by the iodometric spectrophotometric method and by continuous-wave electron paramagnetic resonance. The effect of the exposure was evaluated by measuring cell viability and cellular ROS production following the exposure. The results demonstrate that SOA that aged in the absence of NOx contained more ROS than fresh SOA and were more toxic toward the cells, while varying NOx conditions had no significant influence on levels of the ROS content in fresh SOA and their toxicity. Analysis of ROS in the exposed cells using flow cytometry showed a similar trend with the total ROS content in the SOA. This study provides a first and direct observation of such association.

Exposure to ambient fine particulate matter (PM2.5) is a leading risk factor for the global burden of disease. However, uncertainty remains about PM2.5 sources. We use a global chemical transport model (GEOS-Chem) simulation for 2014, constrained by satellite-based estimates of PM2.5 to interpret globally dispersed PM2.5 mass and composition measurements from the ground-based surface particulate matter network (SPARTAN). Measured site mean PM2.5 composition varies substantially for secondary inorganic aerosols (2.4-19.7 mu g/m(3)), mineral dust (1.9-14.7 mu g/m(3)), residual/organic matter (2.1-40.2 mu g/m(3)), and black carbon (1.0-7.3 mu g/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 mu g/m(3)), industry (6.5 mu g/m(3)), and power generation (5.6 g/m(3)) are leading sources of outdoor global population-weighted PM2.5 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 PM2.5 mass and composition measurements from SPARTAN with the GEOS-Chem model constrained by satellite-based PM2.5 provides insight into sources and processes that influence the global spatial variation in PM2.5 composition.

To date, only a few studies have investigated the potential of coal fly ash particles to trigger heterogeneous ice nucleation in cloud droplets. The presented measurements aim at expanding the sparse dataset and improving process understanding of how physicochemical particle properties can influence the freezing behavior of coal fly ash particles immersed in water.Firstly, immersion freezing measurements were performed with two single particle techniques, i.e., the Leipzig Aerosol Cloud Interaction Simulator (LACIS) and the SPectrometer for Ice Nuclei (SPIN). The effect of suspension time on the efficiency of the coal fly ash particles when immersed in a cloud droplet is analyzed based on the different residence times of the two instruments and employing both dry and wet particle generation. Secondly, two cold-stage setups, one using microliter sized droplets (Leipzig Ice Nucleation Array) and one using nanoliter sized droplets (Welzmann Supercooled Droplets Observation on Microarray setup) were applied.We found that coal fly ash particles are comparable to mineral dust in their immersion freezing behavior when being dry generated. However, a significant decrease in immersion freezing efficiency was observed during experiments with wet-generated particles in LACIS and SPIN. The efficiency of wet-generated particles is in agreement with the cold-stage measurements. In order to understand the reason behind the deactivation, a series of chemical composition, morphology, and crystallography analyses (single particle mass spectrometry, scanning electron microscopy coupled with energy dispersive X-ray microanalysis, X-ray diffraction analysis) were performed with dry- and wet-generated particles. From these investigations, we conclude that anhydrous CaSO4 and CaO - which, if investigated in pure form, show the same qualitative immersion freezing behavior as observed for dry-generated coal fly ash particles - contribute to triggering heterogeneous ice nucleation at the particle-water interface. The observed deactivation in contact with water is related to changes in the particle surface properties which are potentially caused by hydration of CaSO4 and CaO. The contribution of coal fly ash to the ambient population of ice-nucleating particles therefore depends on whether and for how long particles are immersed in cloud droplets.

Obesity and exposure to particular matter (PM) have become two leading global threats to public health. However, the exact mechanisms and tissue-specificity of their health effects are largely unknown. Here we investigate whether a metabolic challenge (early nutritional obesity) synergistically interacts with an environmental challenge (PM exposure) to alter genes representing key response pathways, in a tissue-specific manner. Mice subjected to 7 weeks obesogenic nutrition were exposed every other day during the final week and a half to aqueous extracts of PM collected in the city of London (UK). The expression of 61 selected genes representing key response pathways were investigated in lung, liver, white and brown adipose tissues. Principal component analysis (PCA) revealed distinct patterns of expression changes between the 4 tissues, particularly in the lungs and the liver. Surprisingly, the lung responded to the nutrition challenge. The response of these organs to the PM challenge displayed opposite patterns for some key genes, in particular, those related to the Nrf2 pathway. While the contribution to the variance in gene expression changes in mice exposed to the combined challenge were largely similar among the tissues in PCA1, PCA2 exhibited predominant contribution of inflammatory and oxidative stress responses to the variance in the lungs, and a greater contribution of autophagy genes and MAP kinases in adipose tissues. Possible involvement of alterations in DNA methylation was demonstrated by cell-type-specific responses to a methylation inhibitor. Correspondingly, the DNA methyltransferase Dnmt3a2 increased in the lungs but decreased in the liver, demonstrating potential tissue-differential synergism between nutritional and PM exposure. The results suggest that urban PM, containing dissolved metals, interacts with obesogenic nutrition to regulate diverse response pathways including inflammation and oxidative stress, in a tissue-specific manner. Tissue-differential effects on DNA methylation may underlie tissue-specific responses to key stress-response genes such as catalase and Nrf2. Obesogenic nutrition and air pollution activate inflammation and other stress response pathway in a tissue specific manner, potentially reflecting tissue-specific regulation of DNA methyltransferases.

Atmospheric photooxidation of isoprene forms isoprene epoxydiols (IEPOX) and hydroxymethel-methyl--lactone (HMML) via hydroperoxyl radical (HO2) channel and NO/NO2 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 466ngm(-3). Isoprene SOA tracers correlated well with sulfate (p22 degrees 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/NOx ratio, temperature, and fast heterogeneous reaction of IEPOX in summer. Our study shows that in highly polluted regions like PRD, reduction in SO2 emission can significantly reduce iSOA formation.

Fine particulate matter (PM2.5) air pollution poses a major risk to human health worldwide, and absorbed chemicals play a key role in determining the toxicity of PM2.5. After inhalation and entry into the lungs, PM2.5 components induce pro-inflammatory cytokines (e.g., interleukin (1)-1 beta) in pulmonary cells. To test whether PM2.5 components induce IL-1 beta through signing pathways that include the toll-like receptor 4 (TLR4)/nuclear factor-kappa-gene binding (NF-kappa B), nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3), we exposed the mouse macrophage cell-line RAW264.7 to both water and organic extracts of PM2.5 sampled over a 1-year period in Beijing, China. Varying degrees of oxidative stress and inflammatory responses were induced following exposure, while organic extracts of PM2.5 collected during the heating season induced more significant responses. This response is attributed to high concentrations of polycyclic aromatic hydrocarbons (PAHs) originating from coal combustion and biomass burning for domestic heating. The inhibition of signaling molecules suggested that increased IL-1 beta was associated with the TLR4/NF-kappa B pathway and NLRP3 inflammasome activation, with a slightly difference between water and organic extracts exposure groups, which was likely the result of different chemical components. Our study elucidated a potentially important mechanism by which PM2.5 components could trigger pulmonary inflammation, thus improving our understanding of the deleterious effects of this important and prevalent form of air pollution. (C) 2018 Elsevier Ltd. All rights reserved.

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.

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.

Yinon Rudich responded: It would be beneficial to reach out to other scientific communities and adopt new methods and technologies to atmospheric chemistry. For example, biologists have developed very sensitive tools and assays, that can help address questions relevant to the Anthropocene.

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.

Laboratory studies of atmospheric chemistry characterize the nature of atmospherically relevant processes down to the molecular level, providing fundamental information used to assess how human activities drive environmental phenomena such as climate change, urban air pollution, ecosystem health, indoor air quality, and stratospheric ozone depletion. Laboratory studies have a central role in addressing the incomplete fundamental knowledge of atmospheric chemistry. This article highlights the evolving science needs for this community and emphasizes how our knowledge is far from complete, hindering our ability to predict the future state of our atmosphere and to respond to emerging global environmental change issues. Laboratory studies provide rich opportunities to expand our understanding of the atmosphere via collaborative research with the modeling and field measurement communities, and with neighboring disciplines.

Oxidation of biogenic volatile organic compounds (BVOC) by the nitrate radical (NO3) represents one of the important interactions between anthropogenic emissions related to combustion and natural emissions from the biosphere. This interaction has been recognized for more than 3 decades, during which time a large body of research has emerged from laboratory, field, and modeling studies. NO3-BVOC reactions influence air quality, climate and visibility through regional and global budgets for reactive nitrogen (particularly organic nitrates), ozone, and organic aerosol. Despite its long history of research and the significance of this topic in atmospheric chemistry, a number of important uncertainties remain. These include an incomplete understanding of the rates, mechanisms, and organic aerosol yields for NO3-BVOC reactions, lack of constraints on the role of heterogeneous oxidative processes associated with the NO3 radical, the difficulty of characterizing the spatial distributions of BVOC and NO3 within the poorly mixed nocturnal atmosphere, and the challenge of constructing appropriate boundary layer schemes and non-photochemical mechanisms for use in state-of-the-art chemical transport and chemistry-climate models.This review is the result of a workshop of the same title held at the Georgia Institute of Technology in June 2015. The first half of the review summarizes the current literature on NO3-BVOC chemistry, with a particular focus on recent advances in instrumentation and models, and in organic nitrate and secondary organic aerosol (SOA) formation chemistry. Building on this current understanding, the second half of the review outlines impacts of NO3-BVOC chemistry on air quality and climate, and suggests critical research needs to better constrain this interaction to improve the predictive capabilities of atmospheric models.

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.

The Surface PARTiculate mAtter Network (SPARTAN) is a long-term project that includes characterization of chemical and physical attributes of aerosols from filter samples collected worldwide. This paper discusses the ongoing efforts of SPARTAN to define and quantify major ions and trace metals found in fine particulate matter (PM2.5). Our methods infer the spatial and temporal variability of PM2.5 in a cost-effective manner. Gravimetrically weighed filters represent multi-day averages of PM2.5, with a collocated nephelometer sampling air continuously. SPARTAN instruments are paired with AErosol RObotic NETwork (AERONET) sun photometers to better understand the relationship between ground-level PM2.5 and columnar aerosol optical depth (AOD). We have examined the chemical composition of PM2.5 at 12 globally dispersed, densely populated urban locations and a site at Mammoth Cave (US) National Park used as a background comparison. So far, each SPARTAN location has been active between the years 2013 and 2016 over periods of 2-26 months, with an average period of 12 months per site. These sites have collectively gathered over 10 years of quality aerosol data. The major PM2.5 constituents across all sites (relative contribution +/- SD) are ammoniated sulfate (20% +/- 11 %), crustal material (13.4% +/- 9.9 %), equivalent black carbon (11.9% +/- 8.4 %), ammonium nitrate (4.7% +/- 3.0 %), sea salt (2.3% +/- 1.6 %), trace element oxides (1.0% +/- 1.1 %), water (7.2% +/- 3.3 %) at 35% RH, and residual matter (40% +/- 24 %). Analysis of filter samples reveals that several PM2.5 chemical components varied by more than an order of magnitude between sites. Ammoniated sulfate ranges from 1.1 mu g m(-3) (Buenos Aires, Argentina) to 17 mu g m(-3) (Kanpur, India in the dry season). Ammonium nitrate ranged from 0.2 mu g m(-3) (Mammoth Cave, in summer) to 6.8 mu g m(-3) (Kanpur, dry season). Equivalent black carbon ranged from 0.7 mu g m(-3) (Mammoth Cave) to over 8 mu g m(-3) (Dhaka,

In this study we investigated the possible causal role for soluble metal species extracted from roadway traffic emissions in promoting particulate matter (PM)-induced reactive oxygen species (ROS) production and antioxidant response element (ARE) promoter activation. To this end, these responses have been evaluated in alveolar macrophage and epithelial lung cells that have been exposed to 'Unfiltered', 'Filtered' and 'Filtered + Chelexed' water extracts of PM samples collected from the roadway urban environments of Thessaloniki, Milan and London. Except for Thessaloniki, our results demonstrate that filtration resulted in a minor decrease in ROS activity of the fine PM fraction, suggesting that ROS activity is attributed mainly to water-soluble PM species. In contrast to ROS, ARE activity was mediated predominantly by the water-soluble component of PM present in both the fine and coarse extracts. Further removal of metals by Chelex treatment from filtered water extracts showed that soluble metal species are the major factors mediating ROS and ARE activities of the soluble fraction, especially in the London PM extracts. Finally, utilizing step-wise multiple-regression analysis, we show that 87% and 78% of the total variance observed in ROS and ARE assays, respectively, is accounted for by changes in soluble metal concentration. Using a statistical analysis we find that As, Zn and Fe best predict the ROS-generating/ARE-activating capacity of the near roadway particulate matter in the pulmonary cells studied. Collectively, our findings imply that soluble metals present in roadside PM are potential drivers of both pro and anti-oxidative effects of PM in respiratory tract. (C) 2016 Elsevier Inc. All rights reserved.

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.

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.

Secondary organic aerosol components (SOA) contribute significantly to the activation of cloud condensation nuclei (CCN) in the atmosphere. The CCN activity of internally mixed submicron SOA particles is often parameterized assuming a size-independent single-hygroscopicity parameter . In the experiments done in a large atmospheric reactor (SAPHIR, Simulation of Atmospheric PHotochemistry In a large Reaction chamber, Julich), we consistently observed size-dependent and particle composition for SOA from different precursors in the size range of 50nm-200nm. Smaller particles had higher and a higher degree of oxidation, although all particles were formed from the same reaction mixture. Since decreasing volatility and increasing hygroscopicity often covary with the degree of oxidation, the size dependence of composition and hence of CCN activity can be understood by enrichment of higher oxygenated, low-volatility hygroscopic compounds in smaller particles. Neglecting the size dependence of can lead to significant bias in the prediction of the activated fraction of particles during cloud formation.

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.

Marine viruses constitute a major ecological and evolutionary driving force in the marine ecosystems. However, their dispersal mechanisms remain underexplored. Here we follow the dynamics of Emiliania huxleyi viruses (EhV) that infect the ubiquitous, bloom-forming phytoplankton E. huxleyi and show that EhV are emitted to the atmosphere as primary marine aerosols. Using a laboratory-based setup, we showed that the dynamic of EhV aerial emission is strongly coupled to the host-virus dynamic in the culture media. In addition, we recovered EhV DNA from atmospheric samples collected over an E. huxleyi bloom in the North Atlantic, providing evidence for aerosolization of marine viruses in their natural environment. Decay rate analysis in the laboratory revealed that aerosolized viruses can remain infective under meteorological conditions prevailing during E. huxleyi blooms in the ocean, allowing potential dispersal and infectivity over hundreds of kilometers. Based on the combined laboratory and in situ findings, we propose that atmospheric transport of EhV is an effective transmission mechanism for spreading viral infection over large areas in the ocean. This transmission mechanism may also have an important ecological impact on the large-scale host-virus "arms race" during bloom succession and consequently the turnover of carbon in the ocean.

Heterogeneous neutralization reactions of ammonia and alkylamines with sulfuric acid play an important role in aerosol formation and particle growth. However, little is known about the physical and chemical properties of alkylaminium salts of organic acids. In this work we studied the thermal stability and volatility of alkylaminium carboxylate salts of short aliphatic alkylamines with monocarboxylic and dicarboxylic acids. The enthalpy of vaporization and saturation vapor pressure at 298 K were derived using the kinetic model of evaporation and the Clausius-Clapeyron relation. The vapor pressure of alkylaminium dicarboxylate salts is similar to 10(-6) Pa, and the vaporization enthalpy ranges from 73 to 134 kJ mol(-1). Alkylaminium monocarboxylate salts show high thermal stability, and their thermograms do not follow our evaporation model. Hence, we inferred their vapor pressure from their thermograms as comparable to that of ammonium sulfate (similar to 10(-9) Pa). Further characterization showed that alkylaminium monocarboxylates are room temperature protic ionic liquids (RTPILs) that are more hygroscopic than ammonium sulfate (AS). We suggest that the irregular thermograms result from an incomplete neutralization reaction leading to a mixture of ionic and nonionic compounds. We conclude that these salts are expected to contribute to new particle formation and particle growth under ambient conditions and can significantly enhance the CCN activity of mixed particles in areas where SO2 emissions are regulated

The literature on atmospheric particulate matter (PM), or atmospheric aerosol, has increased enormously over the last 2 decades and amounts now to some 1500-2000 papers per year in the refereed literature. This is in part due to the enormous advances in measurement technologies, which have allowed for an increasingly accurate understanding of the chemical composition and of the physical properties of atmospheric particles and of their processes in the atmosphere. The growing scientific interest in atmospheric aerosol particles is due to their high importance for environmental policy. In fact, particulate matter constitutes one of the most challenging problems both for air quality and for climate change policies. In this context, this paper reviews the most recent results within the atmospheric aerosol sciences and the policy needs, which have driven much of the increase in monitoring and mechanistic research over the last 2 decades. The synthesis reveals many new processes and developments in the science underpinning climate-aerosol interactions and effects of PM on human health and the environment. However, while airborne particulate matter is responsible for globally important influences on premature human mortality, we still do not know the relative importance of the different chemical components of PM for these effects. Likewise, the magnitude of the overall effects of PM on climate remains highly uncertain. Despite the uncertainty there are many things that could be done to mitigate local and global problems of atmospheric PM. Recent analyses have shown that reducing black carbon (BC) emissions, using known control measures, would reduce global warming and delay the time when anthropogenic effects on global temperature would exceed 2 degrees C. Likewise, cost-effective control measures on ammonia, an important agricultural precursor gas for secondary inorganic aerosols (SIA), would reduce regional eutrophication and PM concentrations in large areas of Europe

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<D<1000 nm over a cluster of three mesoscale (similar to 10-100 km) eddies in the North Atlantic. Strongest sensitivity to environmental conditions was found in the 400<D<1000nm size range. In this size range particle concentrations were closely linked to the surface wind speed, indicating in situ production of sea spray aerosols by wind-driven processes. Particle concentrations were also affected by mesoscale variability in oceanic conditions at the vicinity of an anticyclonic eddy. In addition, a distinct aerosol population possibly produced at a distance of similar to 1000-2000 km from the study area was identified. The results highlight the importance of oceanic and atmospheric mesoscale processes in determining the characteristics of aerosols over the marine environment.

The chemical and physical properties of secondary organic aerosol (SOA) formed by the photochemical degradation of biogenic and anthropogenic volatile organic compounds (VOC) are as yet still poorly constrained. The evolution of the complex refractive index (RI) of SOA, formed from purely biogenic VOC and mixtures of biogenic and anthropogenic VOC, was studied over a diurnal cycle in the SAPHIR photochemical outdoor chamber in Julich, Germany. The correlation of RI with SOA chemical and physical properties such as oxidation level and volatility was examined. The RI was retrieved by a newly developed broadband cavity-enhanced spectrometer for aerosol optical extinction measurements in the UV spectral region (360 to 420 nm). Chemical composition and volatility of the particles were monitored by a high-resolution time-of-flight aerosol mass spectrometer, and a volatility tandem differential mobility analyzer. SOA was formed by ozonolysis of either (i) a mixture of biogenic VOC (alpha-pinene and limonene), (ii) biogenic VOC mixture with subsequent addition of an anthropogenic VOC (p-xylene-d(10)), or (iii) a mixture of biogenic and anthropogenic VOC. The SOA aged by ozone/OH reactions up to 29.5 h was found to be non-absorbing in all cases. The SOA with p-xylene-d(10) showed an increase of the scattering component of the RI correlated with an increase of the O / C ratio and with an increase in the SOA density. There was a greater increase in the scattering component of the RI when the SOA was produced from the mixture of biogenic VOCs and anthropogenic VOC than from the sequential addition of the VOCs after approximately the same ageing time. The increase of the scattering component was inversely correlated with the SOA volatility. Two RI retrievals determined for the pure biogenic SOA showed a constant RI for up to 5 h of ageing. Mass spectral characterization shows the three types of the SOA formed in this study have a significant amount of semivolatile components.

Atmospheric absorption by brown carbon aerosol may play an important role in global radiative forcing. Brown carbon arises from both primary and secondary sources, but the mechanisms and reactions of the latter are highly uncertain. One proposed mechanism is the reaction of ammonia or amino acids with carbonyl products in secondary organic aerosol (SOA). We generated SOA in situ by reacting biogenic alkenes (alpha-pinene, limonene, and alpha-humulene) with excess ozone, humidifying the resulting aerosol, and reacting the humidified aerosol with gaseous ammonia. We determined the complex refractive indices (RI) in the 360-420 nm range for these aerosols using broadband cavity enhanced spectroscopy (BBCES). The average real part (n) of the measured spectral range of the NH3-aged alpha-pinene SOA increased from n = 1.50 (+/- 0.01) for the unreacted SOA to n = 1.57 (+/- 0.01) after 1.5 h of exposure to 1.9 ppm NH3, whereas the imaginary component (k) remained below k <0.001 ((+0.002)(-0.001)) For the limonene and alpha-humulene SOA the real part did not change significantly, and we observed a small change in the imaginary component of the RI. The imaginary component increased from k = 0.000 to an average k = 0.029 (+/- 0.021) for alpha-humulene SOA, and from k <0.001((+0.002)(-0.001)) to an average k = 0.032 (+/- 0.019) for limonene SOA after 1.5 h of exposure to 1.3 and 1.9 ppm of NH3, respectively. Collected filter samples of the aged and unreacted alpha-pinene SOA and limonene SOA were analyzed off-line by nanospray desorption electrospray ionization high resolution mass spectrometry (nano-DESI/HR-MS), and in situ using a Time-of-Flight Aerosol Mass Spectrometer (ToF-AMS), confirming that the SOA reacted and that various nitrogen-containing reaction products formed. If we assume that NH3 aging reactions scale linearly with time and concentration, which will not necessarily be the case in the atmosphere, then a 1.5 h reaction with 1 ppm NH3 in the laboratory is e

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.

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.

One of the major uncertainties in the understanding of Earth's climate system is the interaction between solar radiation and aerosols in the atmosphere. Aerosols exposed to high humidity will change their chemical, physical, and optical properties due to their increased water content. To model hydrated aerosols, atmospheric chemistry and climate models often use the volume weighted mixing rule to predict the complex refractive index (RI) of aerosols when they interact with high relative humidity, and, in general, assume homogeneous mixing. This study explores the validity of these assumptions. A humidified cavity ring down aerosol spectrometer (CRD-AS) and a tandem hygroscopic DMA (differential mobility analyzer) are used to measure the extinction coefficient and hygroscopic growth factors of humidified aerosols, respectively. The measurements are performed at 80% and 90%RH at wavelengths of 532 nm and 355 nm using size-selected aerosols with different degrees of absorption; from purely scattering to highly absorbing particles. The ratio of the humidified to the dry extinction coefficients (fRH(ext)(%RH, Dry)) is measured and compared to theoretical calculations based on Mie theory. Using the measured hygroscopic growth factors and assuming homogeneous mixing, the expected RIs using the volume weighted mixing rule are compared to the RIs derived from the extinction measurements. We found a weak linear dependence or no dependence of fRH(%RH, Dry) with size for hydrated absorbing aerosols in contrast to the non-monotonically decreasing behavior with size for purely scattering aerosols. No discernible difference could be made between the two wavelengths used. Less than 7% differences were found between the real parts of the complex refractive indices derived and those calculated using the volume weighted mixing rule, and the imaginary parts had up to a 20% difference. However, for substances with growth factor less than 1.15 the volume weighted mixing rule assumptio

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

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.

Aerosols containing biological components can have a significant effect on human health by causing primarily irritation, infection and allergies. Specifically, airborne fungi can cause a wide array of adverse responses in humans depending on the type and quantity present. In this study we used chemical biomarkers for analyzing fungi-containing aerosols in the eastern Mediterranean region during the year 2009 in order to quantify annual fungal abundances. The prime marker for fungi used in this study was ergosterol, and its concentrations were compared with those of mannitol and arabitol which were recently suggested to also correlate with fungal spores concentrations (Bauer et al., 2008a). Back trajectory analysis, inorganic ions, humidity and temperature were used in an attempt to identify sources as well as the dependence on seasonal and environmental conditions. We found that the ambient concentrations of ergosterol, arabitol and mannitol range between 0 and 2.73 ng m(-3), 1.85 and 58.27 ng m(-3), 5.57 and 138.03 ng m(-3), respectively. The highest levels for all biomarkers were during the autumn, probably from local terrestrial sources, as deduced from the inorganic ions and back trajectory analysis. Significant correlations were observed between arabitol and mannitol during the entire year except for the winter months. Both sugars correlated with ergosterol only during the spring and autumn. We conclude that mannitol and arabitol might not be specific biomarkers for fungi and that the observed correlations during spring and autumn may be attributed to high levels of vegetation during spring blossoms and autumn decomposing.

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

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.

Atmospheric aerosols scatter and absorb solar radiation leading to variable effects on Earth's radiative balance. Aerosols individually comprising mixtures of different components ("internally mixed") interact differently with light than mixtures of aerosols, each comprising a different single component ("externally mixed"), even if the relative fractions of the different components are equal. In climate models, the optical properties of internally mixed aerosols are generally calculated by using electromagnetic "mixing rules", which average the refractive indices of the individual components in different proportions, or by using coated-sphere Mie scattering codes, which solve the full light scattering problem assuming that the components are divided into two distinct layers. Because these calculation approaches are in common use, it is important to validate them experimentally. In this article, we present a broad perspective on the optical properties of internally mixed aerosols based on a series of laboratory experiments and theoretical calculations. The optical properties of homogenously mixed aerosols comprised of non-absorbing and weakly absorbing compounds, and of coated aerosols comprised of strongly absorbing, non-absorbing, and weakly absorbing compounds in different combinations are measured using pulsed and continuous wave cavity ring down aerosol spectrometry (CRD-AS). The success of electromagnetic mixing rules and Mie scattering codes in reproducing the measured aerosol extinction values is discussed.

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.

Atmospheric humic-like substances (HULIS) constitute a major fraction of the water soluble organic carbon of aerosol particles. We investigated sorption and desorption of water and two model organic contaminants (toluene and benzyl alcohol) on HULIS and a standard humic substance (Suwannee River fulvic acid; SRFA) under varying relative humidity using a quartz crystal microbalance. Simultaneous sorption of water and benzyl alcohol (capable of specific interactions like hydrogen bonding or charge transfer) on HULIS and SRFA shows significant, humidity-dependent, cooperative sorption at intermediate water activity, as well as a dependence of sorption distribution coefficient on the wetting-drying pathway. In contrast sorption of toluene (capable of only nonspecific interactions) was humidity-independent. Atmospheric HULIS is thus found to have several sorption features in common with terrestrial and aquatic humic substances and soil organic matter. These features are consistent with the link solvation model (LSM), whereby water assists in cooperative sorption of specifically interacting compounds by the organic matter sorbent, and subsequent changes in sorbent structure result in sorption hysteresis. Sorption of compounds capable of only nonspecific interactions is unaffected by hydration status. Such sorption features can lead to considerable uncertainty in predicting and modeling transport of organic pollutants in the atmosphere.

We compare a full-year (2006) record of surface air NO2 concentrations measured in Israeli cities to coinciding retrievals of tropospheric NO2 columns from satellite sensors (SCIAMACHY aboard ENVISAT and OMI aboard Aura). This provides a large statistical data set for validation of NO2 satellite measurements in urban air, where validation is difficult yet crucial for using these measurements to infer NOx emissions by inverse modeling. Assuming that NO2 is well-mixed throughout the boundary layer (BL), and using observed average seasonal boundary layer heights, near-surface NO2 concentrations are converted into BL NO2 columns. The agreement between OMI and (13:45) BL NO2 columns (slope=0.93, n=542), and the comparable results at 10:00 h for SCIAMACHY, allow a validation of the seasonal, weekly, and diurnal cycles in satellite-derived NO2. OMI and BL NO2 columns show consistent seasonal cycles (winter NO2 1.6-2.7x higher than summer). BL and coinciding OMI columns both show a strong weekly cycle with 45-50% smaller NO2 columns on Saturday relative to the weekday mean, reflecting the reduced weekend activity, and validating the weekly cycle observed from space. The diurnal difference between SCIAMACHY (10:00) and OMI (13:45) NO2 is maximum in summer when SCIAMACHY is up to 40% higher than OMI, and minimum in winter when OMI slightly exceeds SCIAMACHY. A similar seasonal variation in the diurnal difference is found in the source region of Cairo. The surface measurements in Israel cities confirm this seasonal variation in the diurnal cycle. Using simulations from a global 3-D chemical transport model (GEOS-Chem), we show that this seasonal cycle can be explained by a much stronger photochemical loss of NO2 in summer than in winter.

Surfactants often found in tropospheric aerosols, can affect the onset and development of clouds. Due to high dilution during droplet growth, the effects of surfactants on cloud microphysical processes have been mostly neglected. However, while cloud growth by coalescence conserves the combined volume of all cloud droplets, it reduces the combined surface area. This could lead to enrichment of water-insoluble surfactants (WIS) and to reduced surface tension of droplets forming in warm processes. Measurements of individual raindrops reveal the presence of water insoluble surfactants. Our field and laboratory studies as well as simple theoretical arguments suggest that by causing varying and size-dependent surface tension, WIS can affect cloud microphysics.

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.

Cavity ring down aerosol extinction measurements are combined with size distribution measurements to provide a multiparameter basis for the retrieval of the aerosol complex refractive index. We show that two distinct size distributions of small particles (<300 nm) suffice to obtain robust convergence of the Mie theory fit of the extinction function. Experiments are performed both for purely scattering and for absorbing aerosol. Thus this method provides a perspective to use cavity ring down aerosol spectroscopy in field and laboratory measurements that often suffer from low particle concentrations and a lack of large particles.

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.

Levoglucosan is a tracer for biomass burning sources in atmospheric aerosol particles. Therefore, much effort has been recently put into developing methods for its quantification. This review describes and compares both established and emerging analytical methods for levoglucosan quantification in ambient aerosol samples, with the special needs of the environmental analytical chemist in mind.

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.

Heterogeneous reactions of oleic acid aerosol particles with ozone are studied below 1% relative humidity. The particles have inert polystyrene latex cores (101-nm diameter) coated by oleic acid layers of 2 to 30 nm. The chemical content of the organic layer is monitored with increasing ozone exposure by using an aerosol mass spectrometer. The carbon-normalized percent yields of particle-phase reaction products are 20-35% 9-oxononanoic acid, 1-3% azelaic acid, 1-3% nonanoic acid, and 35-50% other organic molecules (designated as CHOT). There is approximately 25% evaporation, presumably as 1-nonanal. To explain the formation of CHOT molecules and the low yields of azelaic and nonanoic acids, we suggest a chemical mechanism in which the Criegee biradical precursors to azelaic acid and nonanoic acid are scavenged by oleic acid to form CHOT molecules. These chemical reactions increase the carbon-normalized oxygen content (z/x) of the CxHyOz layer from 0.1 for unreacted oleic acid to 0.25 after high ozone exposure. Under the assumption that oxygen content is a predictor of hygroscopicity, our results suggest an increased cloud condensation nuclei activity of atmospherically aged organic particles that initially have alkene functionalities.

Relative humidity (RH) history and chemical composition determine whether atmospheric particles are liquid or solid. Particle physical state affects many climatic and environmental phenomena such as radiative transfer, visibility, and heterogeneous chemistry. Here we report the crystallization RH (CRH) at 293 K of particles throughout the entire sulfate-nitrate-ammonium composition space, and the new laboratory data are expressed as an empirical polynomial. Particles with compositions close to ammonium sulfate crystallize near 30% RH. Such particles are common in the boundary layer, including the eastern USA and East Asia though not Europe. Our measurements show the formation of several solids within the same particle for compositions enriched in nitrate or somewhat acidic, although the CRH is under 30%. The CRH for homogeneous nucleation is 40 to 55% below the deliquescence RH (DRH) for most chemical compositions. Our new results provide essential data for the incorporation of particle physical state in global models of chemistry and climate.

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.

The reactive uptake of Cl and Br atoms by closely packed organic thin films was studied in a flow reactor. For Cl, the reactive uptake coefficient, gamma, was near collision rate for alkane and alkene surfaces. For Br, gamma =(3 +/- 1) X 10(-2) for alkane and gamma=(5 +/- 2) X 10(-2) for alkene surfaces. The processing of the surface was monitored using FTIR, XPS and contact angle measurements. Oxidized surface-bound products and a concurrent increase in hydrophilicity were observed. The probability of a reactive collision between Br, Cl, O(P-3), O-3 and NO3 and surface-bound organics is compared with that of comparable gasphase reactions, showing that reactions with a high activation energy in the gas-phase have an enhanced surface reaction probability. The uptake coefficients for these tropospheric oxidants are used to estimate the processing time for an organic coated aerosol.

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.

Uptake measurements of ozone were conducted with two types of proxies for atmospheric organic aerosols: organic liquids and self-assembled organic monolayers. Alkanes and terminal alkenes were used. The monolayer surface was characterized, prior to and after reaction, using IR spectroscopy. Uptake experiments were conducted using a flow tube reactor coupled to a chemical ionization mass spectrometer. The reactive uptake coefficient, gamma, is shown to be due to reaction with the double bond. For the monolayers, gamma is composed solely of a surface reactive component and is smaller by at least an order of magnitude than values obtained for a liquid of the same chain length. Uptake by the liquids is higher due to solubility and reaction ill the bulk. The phase of the atmospheric organic aerosol will determine the appropriate use of a bulk or surface uptake probability in atmospheric models. Since the aerosol surface is processed and sites are consumed, gamma is time variant. We define a parameter gamma' as the surface uptake probability per reactive site and determine its value as 9 x 10(-19) cm(2) molecule(-1). This enables the modeling of surface reactions as surface site concentrations diminish following interaction with the gaseous species.

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 reactive uptake coefficients (γ) of NO onto pure water and dilute solutions of NaCl, NaBr, and NaNO were measured using a wetted‐wall flow‐tube setup combined with a long‐path absorption cell for the detection of NO. The measured γ values were in the range 1.5 × 10 – 6 × 10, depending on the salt concentration in the water. By measuring γ as a function of salt concentration, H for NO in water was determined to be (1.9 ± 0.4) × 10 atm cm s at 273 K, assuming that the rate coefficient for the reaction of NO with Cl is 2.76 × 10 s at 273 K. The Henry's law coefficient for NO in water is estimated to be 0.6 ± 0.3 atm, assuming that the diffusion coefficient of NO in water is = (1.0 ± 0.5) × 10 cm s. Uptake of NO on pure water is interpreted as due to reaction of NO with HO to produce HNO and OH in the liquid phase. Implications of these findings to the chemistry of NO in the troposphere are also discussed.

The reactions of oxygen atoms in their triple and singlet states with hydrocarbon clusters were investigated. The results indicate that some liquid‐type effects can be demonstrated already in the reactions of small clusters. Two examples are discussed: (1) The reaction of O( 3 P ) with cyclohexane in which a single ‘‘solvent molecule’’ is enough to reproduce the products of the liquid reaction. (2) The reactions of O( 1 D ) with methane clusters for which the translational, vibrational, rotational, spin‐orbit, and Λ‐doubling state populations were analyzed, on‐statistical distributions are observed even for the reaction of large methane clusters. The results of these studies are discussed in terms of non‐adiabatic effects induced by the long lived collision complex.

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.