לוח שנה משולב

Conventional wisdom says that atmospheric oxidation is entirely photochemical and mainly driven by the OH radical, with sunlight, ozone and water vapor as the key ingredients. That description is appropriate for summertime conditions with ample sunlight and high relative humidity. However, recent laboratory studies and field observations have identified other mechanisms for the generation of atmospheric free radicals that challenge the traditional picture, especially in the winter and in polluted environments. These cycles are driven by the availability of nitrogen oxides, common pollutants that are byproducts of combustion, and by reactions of these compounds on surfaces. Dinitrogen pentoxide, N2O5, forms in the dark from oxidation of NO2 by O3. It reacts heterogeneously with aerosol particles that contain chloride to activate photo-labile halogens in the form of nitryl chloride, ClNO2. Nitrous acid, HONO, forms heterogeneously from direct uptake of NO2, predominantly to ground, rather than aerosol surface. Rapid photolysis of this compound after sunrises provides a large but variable OH radical source. Both of these dark, heterogeneous processes influence regional oxidant budgets, but in substantially different ways and with different impacts for both air quality and climate. This seminar will examine the current understanding of such unconventional free radical sources based on recent field and laboratory studies.

We review recent progress in understanding Quantum Field Theory. The new results connect three thorny and fundamental questions: The symmetries of second order phase transitions, monotonicity of the renormalization group flow, and the entanglement entropy of the vacuum. We give examples of various applications for theories ranging from boiling water to Quantum Chromodynamics.