(19c) Heterogeneous Chemistry of Organic Compounds on Atmospheric Droplets

The mass transfer of aromatic hydrocarbon vapors to water droplets in air was studied in the presence of ozone in the gas phase. A falling droplet reactor with water droplets of diameters 55 to 182 mm was used for the study. Ozone reacted with the organic compound at the air-water interface, thereby decreasing the mass transfer resistance and increasing the rate of uptake into the droplet. A Langmuir-Hinshelwood reaction mechanism at the air-water interface satisfactorily described the surface reaction. The first order surface reaction rate constant, showed a distinct dependence on the droplet size. Several organic intermediates were identified in the aqueous phase as a result of ozonation of naphthalene and phenanthrene vapors at the surface of the droplet indicating both peroxidic and non-peroxidic routes for ozonation. The presence of an organic carbon surrogate (Fulvic acid) increased both the partition constant of the organic and the surface reaction rate of ozone.