Kinetics of Heterogeneous Reaction of Ozone with Oleic Acid and Its Dependence on Droplet Size, Relative Humidity, and Ozone Concentration

In this study, the heterogeneous reaction of oleic acid droplets with gas-phase ozone was studied by an ATR-FTIR flow reactor. The effects of droplet size, relative humidity, and ozone concentration on the reaction kinetics were carefully investigated. Specifically, the pseudo-first-order rate constant kapp and the uptake coefficient γ displayed a size dependence, with kapp decreasing from ~4.5 × 10−3 to ~3.2 × 10−3 and γ linearly increasing from ~4.4 × 10−5 to ~3.2 × 10−4 as the suspended droplet diameter increased from 0.1 to 1.0 μm. It is believed that the reaction kinetics were the major contributor to the reactive uptake in the reaction between the oleic acid droplets and gas-phase ozone observed in this study. In addition, RH showed no obvious influence on the heterogeneous reaction kinetics, in agreement with findings from previous studies. Furthermore, the kapp was found to display a Langmuir–Hinshelwood dependence on the gas-phase ozone concentration with KO3 = (3.29 ± 0.46) × 10−15 molecules cm−3 and k[S] = 0.153 ± 0.007 s−1, which is consistent with observations of the ozonolysis of unsaturated organic materials in the literature. Kinetics data related to the heterogeneous reaction of ozone and oleic acid under different conditions could be used in chemistry transport models and air quality models to better understand air pollutants’ adverse health impacts.