Sensitivity of photochemical surface ozone formation regimes to emissions and meteorology in India

Abstract. Atmospheric aerosols significantly contribute to air pollution and influence atmospheric chemistry, impacting air quality and public health. Decrease in aerosols can hinder the radical uptake sink of HO2, and thus increase NOx and OH, and subsequently increase ozone levels. This study investigates the seasonal variations of PM10 and aerosol surface area and their effect on surface ozone levels in India, using the GEOS-Chem Chemical Transport Model for the years 2018 and 2022, two years with high and low simulated PM10 concentrations, respectively. The results reveal substantial seasonal variations in PM10 and aerosol surface area. In winter (DJF), higher PM10 and aerosol surface area in the Indo-Gangetic Plain (IGP) and western Central India (CI) result from biomass burning and industrial activity, while coastal regions show lower aerosol surface area. A decrease in aerosol surface area is seen during the pre-monsoon (March–April–May; MAM) and monsoon (June–July–August–Septmember; JJAS), followed by an increase in the post-monsoon (ON) season. As a result, aerosol-induced HO2 uptake during winter and post-monsoon suppress surface ozone by approximately 5–10 µg m−3 in 2022 when compared to that of 2018. In contrast, during monsoon in 2022, the decrease in aerosol surface area caused an ozone increase of 5–7.5 µg m−3 when compared to that of 2018. On average, this increase in surface ozone due to the decrease in aerosols can be mitigated by reducing anthropogenic NOx emissions by about 25 %–50 %. Thus, we recommend integrated strategies addressing aerosols, precursor emissions and regional meteorology to combat ozone pollution.