Impacts of wildfire smoke aerosols on near-surface ozone photochemistry

Abstract. Wildfires have been an increasing concern for the environment, yet the ozone (O₃) production from wildfires remains poorly characterized. Here, we aim to elucidate the role of aerosols from wildfire smoke in near-surface O₃ photochemistry by integrating insights from 0-D box model (F0AM) to 3-D chemical transport model (GEOS-Chem). While smoke aerosols typically inhibit O₃ production through heterogeneous chemical and radiative pathways, we find that the positive effects of precursor emissions outweigh the negative effects of aerosols for most fires. The relative importance of the two aerosol effects varies, with the heterogeneous chemical effect generally overshadowing the radiative effect in the far field of fires. However, near the sources of extremely large fires, the radiative effect dominates, leading to an overall suppression of O₃ production. By assessing the chain termination of hydrogen oxide radicals (HO_x) and introducing the “light-limited” regime determination in GEOS-Chem, we find that a significant portion of O₃ production occurred within light-limited and heterogeneous chemistry-inhibited regimes during the 2020 wildfire season in California. Building on the discovery that both aerosol and nitrogen oxide (NO_x) concentrations modulate aerosol influence, we demonstrate that the surface PM_2.5 to tropospheric NO₂ column ratio—a metric retrievable from satellite—can serve as an indicator for identifying aerosol-dominated regimes through observations.