Field measurements have shown that organic material is abundant in the atmosphere. Pure organic particulate matter can consist most likely of a variety of organic compounds which may form in some cases multiphase mixtures. Organic particles while in the atmosphere can be oxidized by trace gas species such as O3 and NO3. This could potentially lead to the modification of the particle composition and possibly lead to volatilization. To better understand the oxidation of organic particles, we investigate the reaction of O3 with lauric acid/oleic acid, myristic acid/oleic acid, and multicomponent mixtures representing closely the composition of meat cooking aerosols. To address possible volatilization of organic aerosols we study the oxidation of organic substrates by NO3 radicals. Self assembled monolayers serve as a proxy for an organic aerosol particle. These experiments are performed using a rotating-wall flow-tube reactor coupled to a chemical ionization mass spectrometer (CIMS). Changes in surface properties are determined using X-ray photoelectron spectroscopy (XPS).

Surface-active organic molecules (organic molecules that have both a hydrophobic group and a hydrophilic group) are common constituents of tropospheric aerosol particles. Several researchers have suggested that these organic molecules form organic coatings or films on the surface of aqueous particles in the troposphere. Here, we investigate the effect of insoluble organic monolayers consisting of straight-chain surfactants (1-hexadecanol, 1-octadecanol, and stearic acid) and branched surfactants (phytanic acid) on the hydrolysis of N2O5 by aqueous H2SO4 surfaces. A newly developed rectangular channel flow reactor coupled to CIMS is used to study the hydrolysis of N2O5. The reactive uptake coefficient decreased by approximately a factor of 17-61 in the presence of insoluble, straight-chain organic monolayers compared to uncoated solutions. In contrast to the straight-chain data, N2O5 uptake in the presence of phytanic acid did not have a signifficant effect on the N2O5 reactive uptake coefficient. In addition to measuring the reactive uptake coefficients, we also investigated the relationship between properties of the monolayers and the reactive uptake coefficients. The reactive uptake coefficients measured on aqueous sulfuric acid subphases show a relationship to the surface area occupied by the surfactant molecules.