Ozonolysis of oleic acid adsorbed to polar and nonpolar aerosol particles.

Single-particle kinetic studies of the reaction between oleic acid and O-3 have been conducted on two different types of core particles: polystyrene latex (PSL) and silica. Oleic acid was found to adsorb to both particle types in multilayer islands that resulted in an adsorbed layer of a total volume estimated to be less than one monolayer. The rate of the surface reaction between surface-adsorbed oleic acid and O-3 has been shown for the first time to be influenced by the composition of the aerosol substrate in a mixed organic/inorganic particle. A Langmuir-Hinshelwood mechanism was applied to the observed dependence of the pseudo-first-order rate constant with [O-3], and the resulting fit parameters for the ozone partition coefficient (K-O3) and maximum first order rate constant (k(1,max)) suggest that the reaction proceeded faster on the less polar PSL core at lower [O-3] due to the increased residence time of O-3 on the PSL surface, but the reaction was ultimately more efficient on the silica surface at high [O-3]. Values for the uptake coefficient, gamma(oleic), for reaction of oleic acid on PSL spheres decrease from 2.5 x 10(-5) to 1 x 10(-5) with increasing [O-3] from 4 to 25 ppm and overlap at high [O-3] with the estimated values for gamma(oleic) on silica, which decrease from 1.6 x 10(-5) to 1.3 x 10(-5). The relationship between gamma(oleic) and the more common expression for gamma(o3), is discussed.