Exploring potential impacts of Black Carbon on vertical mixing and overall air quality over Northern India

Black Carbon (BC) particles from incomplete combustion perturb the Earth's energy balance by absorbing solar radiation and modifying cloud microphysics. Previous studies have shown that Indian BC emissions significantly impact the summer monsoon, regional climate, and human health. Studies over China have reported that high BC concentrations absorb sufficient radiation to influence planetary boundary layer (PBL) vertical stability and mixing, and can significantly affect overall near-surface air quality. Such effects may have important implications for mitigation efforts that aim to improve regional air quality and climate. Here, we explore BC during extreme pollution events over India, using the WRF-Chem Chemistry Transport Model v4.2 with the MOSAIC sectional aerosol scheme at a horizontal resolution of 12 km × 12 km. The model is able to capture elevated PM_2.5 concentrations (~300 μg m^-3) over the Indo-Gangetic Plain and localised hotspots over some major megacities. To isolate contributions of emissions from anthropogenic and biomass burning sources to the overall air quality, we perform a base simulation and sensitivity experiments. We analyse the diurnal evolution of vertical profiles of BC and PM2.5 in the PBL. We focus on the factors that control these distributions and compare our results with available observations to evaluate the model. Diurnal PBL dynamics strongly influence temporal and spatial variations in aerosol concentrations. We investigate the role of BC in influencing the PBL dynamics during high pollution events, and hence overall air quality by perturbing the vertical radiation, temperature, and stability profiles.