Aerosol Inhibition on Photochemical Surface Ozone Formation in Present Day and Under Future Climate and Air Quality Scenarios

G.S. Gopikrishnan, DANIEL WESTERVELT, Jayanarayanan Kuttippurath, Columbia University

     Abstract Number: 249
     Working Group: Aerosol Processes and Properties in Changing Environments in the Anthropocene

Abstract
Aerosols significantly influence tropospheric oxidation and ozone formation by modulating photolysis rates and radical sinks. This study employs the GEOS-Chem model to analyze different aerosol heterogeneous uptake coefficients (0, 0.1, 0.2 and 0.4) and their effects on photochemical ozone levels across global regions under future Shared Socioeconomic Pathways (SSP) scenarios. Lower uptake coefficients lead to an increase in the concentration of radical species like HO2 and reduce the extent of aerosol-inhibited regime (AIR) in regions such as India and East Asia which are currently within AIR, leading to a notable increase in surface ozone (40–50%), particularly during colder months. Projections for 2046 indicate a global reduction in AIR, resulting from stricter emission controls. By 2096, the extent of AIR further diminishes, with regions like Southeast Asia transitioning to NOx-limited conditions, though aerosol uptake of HO2 continues to elevate surface ozone levels by 10–15% in heavily aerosol-loaded areas. In India, during monsoon in 2022, the decrease in aerosol surface area caused an ozone increase of 10–20 μg/m³ when compared to that of 2018. On average, eighty percent of this increase in surface ozone due to reduction in PM can be mitigated by reducing anthropogenic NOx emissions by 25–50%. Thus, we recommend integrated strategies addressing aerosols, precursor emissions and regional meteorology to combat ozone pollution.