Disentangling the Separate and Combined Effects of Aerosol‐Radiation and Aerosol‐Photolysis Interactions on Air Quality Over India

Abstract This study examines the individual and combined impacts of aerosol‐radiation interactions (ARI) and aerosol‐photolysis interactions (API) on regional air quality over India using the WRF‐Chem model for May 2018. Model performance was validated against CERES, MERRA‐2, and CPCB observations, demonstrating good agreement in simulating key meteorological variables and air pollutants. Results show that ARI increases mean PM 2.5 concentrations by approximately 3 μg/m 3 (12.4%) across India by reducing surface shortwave radiation and enhancing atmospheric stability, which limits pollutant dispersion. In contrast, API reduces PM 2.5 by about 1.8 μg/m 3 (7.2%) due to lower photolysis rates, which suppress secondary aerosol formation. When combined, ARI and API lead to a net PM 2.5 increase of around 2 μg/m 3 (8.4%). Simultaneously, surface O 3 levels decrease under all scenarios: by 2.6 ppbv (4%) with ARI, 1.7 ppbv (2.6%) with API, and 1.2 ppbv (1.8%) when both effects are included. These results underscore the complex interplay between aerosols, atmospheric stability, and chemical processes. They highlight the need for integrated air quality strategies that account for both direct emissions and feedback effects from aerosol interactions, especially in regions with diverse emission sources like India.