Implications of this effect and of H2O2 surface accumulation on photochemistry at the airewater interface of atmospheric droplets

Experiments are conducted to determine the effect of a cage ofwatermolecules on the photolysis quantum yields of nitrate, FeOH2þ, and H2O2. Results suggest that the quantum yields of nitrate and FeOH2þ are decreased by the recombination of photo-fragments ( OH þ NO2 and Fe2þ þ OH, respectively) before they leave the surrounding cage of water molecules. However, no evidence is found for an enhanced quantum yield for H2O2. Therefore, the photolysis of nitrate and FeOH2þ could be enhanced if the cage of the solvent molecules is incomplete, as is the case at the airewater interface of atmospheric droplets. The photolysis rate constant distribution within nitrate, FeOH2þ, and H2O2 aerosols is calculated by combining the expected quantumyield data in the bulk and at the interfacewithMie theory calculations of light intensity. The photolysis rate constant of nitrate and FeOH2þ would be significantly higher at the surface than in the bulk if quantum yields are enhanced at the surface. In the case of H2O2, the photolysis rate constant would be enhanced by surface accumulation. The results concerning the expected rates of photolysis of these photoactive species are applied to the assessment of the reaction between benzene and OH in the presence of OH scavengers in an atmospherically relevant scenario. For a droplet of 1 mm radius, a large fraction of the total OH-benzene reaction (15% for H2O2, 20% for nitrate, and 35% for FeOH2þ) would occur in the surface layer, which accounts for just 0.15% of the droplet volume. 2010 Elsevier Ltd. All rights reserved.