AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Change in Reactivity of Organic Aerosols toward Heterogeneous OH Oxidation over Reaction Time
Man Mei Chim, Christopher Lim, Jesse Kroll, MAN NIN CHAN, The Chinese University of Hong Kong
Abstract Number: 27 Working Group: The Air We Breathe: Indoor Aerosol Sources and Chemistry
Abstract Oxidation initiated at or near a particle surface by gas-phase oxidants can continuously change the composition and properties of organic particles, which in turn alter the heterogeneous reactivity over time. However, chemical transformation of organic particles by heterogeneous oxidation is typically described by a single kinetic parameter (effective OH uptake coefficient, γeff), which implicitly assumes the reactivity does not change significantly over their atmospheric lifetimes. Using time-resolved particle composition and size data measured in an environmental chamber, we find that the heterogeneous reactivity of citric acid toward gas-phase OH radicals continuously decreases over reaction time and slows down by 16% after oxidation equivalent to about 2 days of OH exposure. This could be explained by consumption of citric acid, and its concentration at the particle surface drops due to OH oxidation and the formation of reaction products during oxidation. This lowers the reactive collision probability between citric acid and gas-phase OH radicals at the gas–particle interface, leading to a smaller overall reactivity. The results suggest that the use of a single kinetic parameter could overpredict the heterogeneous OH oxidative loss rate of citric acid and other organic compounds over their atmospheric time scales.