Novel Triple-Oxygen Isotope Study Indicates Unprecedented Ozone-Particulate Interaction Pathways in Atmospheric Pollution Chemistry.

Ozone plays a fundamental role in the chemistry of the atmosphere, mediating oxidation reactions in phases and at phase boundaries. Here, we investigate the least-explored solid-phase heterogeneous processes involving ozone to understand the reaction pathways of O3 with airborne aerosols. Using triple oxygen isotope ratios as tracers, we found that the ozone reaction oxidizes organic particles and produces carbon dioxide, with oxygen atoms largely from O3. Along with the formation of CO2, an equal amount of O2 from water decomposition is inferred. Chemical reaction kinetics, however, is yet to be identified. One hypothetical pathway is through Criegee intermediates, formed by the reaction of ozone with aldehyde/ketone-like organic compounds (unsaturated hydrocarbons) catalyzed by metal oxides. Inclusion of the process in a chemistry-transport model could yield a significant change in the ozone budget. The study shows the importance of ozone-induced heterogeneous chemical reactions on aerosol surfaces occurring in polluted atmospheres.