Regional Sensitivity of Ozone Formation to Emissions and Meteorology in India

Atmospheric aerosols play a key role in air pollution and atmospheric chemistry, with important consequences for air quality and public health. Variations in aerosol loading influence heterogeneous chemistry by regulating the uptake of HO₂ radicals on particle surfaces; a reduction in aerosols weakens this sink, enhances NOx and OH concentrations, and consequently increases surface ozone. This study investigates the seasonal variability of PM₁₀ and aerosol surface area and their impact on surface ozone over India using the GEOS-Chem chemical transport model for 2018 and 2022, representing years with high and low simulated PM₁₀ concentrations, respectively. The results show pronounced seasonal variations in both PM₁₀ and aerosol surface area. During winter (DJF), elevated PM₁₀ and aerosol surface area are observed over the Indo-Gangetic Plain and western Central India, mainly driven by biomass burning and industrial activities, while coastal regions show relatively lower aerosol surface area. Aerosol surface area decreases during the pre-monsoon (MAM) and monsoon (JJAS) seasons, followed by an increase during the post-monsoon (ON) period. Enhanced aerosol surface area during winter and post-monsoon leads to stronger aerosol-induced HO₂ uptake, suppressing surface ozone by approximately 5–10 μg/m³ in 2022 compared to 2018. In contrast, during the monsoon season, the reduced aerosol surface area in 2022 results in an increase in surface ozone of about 5–7.5 μg/m³ relative to 2018. On average, this aerosol-driven enhancement in surface ozone can be mitigated by reducing anthropogenic NOx emissions by roughly 25–50%. These findings emphasise the importance of integrated air quality management strategies that jointly address aerosol levels, precursor emissions, and regional meteorological conditions to effectively control ozone pollution over India.