Atmospheric Sciences Division Seminar

Atmospheric aerosol particles host a very complex mixture of organic and inorganic components. A significant fraction of organics present in aerosol particles are surface active, such as linear alkanoic and alkenoic acids or aromatics with hydrophilic substituents. Using reasonably well defined proxy systems, we have started to look at three different aspects of organic coatings: first, they may establish a barrier towards the transfer of trace gases from the gas phase into the aerosol phase. We have used the fast uptake of nitric acid to deliquesced NaCl particles to probe the effect of long chain C9 to C18 saturated and unsaturated fatty acids, indicating that the monolayer forming properties of these fatty acids determines the degree of reduction of phase transfer of nitric acid to the aqueous particles. Second, the chemical environment in a coating is substantially different from that in either the pure organic or the aqueous bulk phases. This is demonstrated with ozonolysis studies of oleic acid monolayers on deliquesced NaCl particles, which shows substantial formation of H2O2, exceeding that from bulk oleic acid ozonolysis or that known from alkene oxidation in the gas phase. Third, a number of species in organic coatings are absorbing light in the visible and UVA wavelength range. We have specifically investigated photosensitized redox processes that lead, among other things, to light induced reaction of organics with nitrogen dioxide and ozone, the former becoming a substantial source of nitrous acid in the lowermost troposphere.