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.