Understanding Gaseous and Particulate Air Pollutants in India

South Asia is one of most polluted region on the planet. Severe haze events occur frequently in India with the annual particulate matter (PM) concentration level three times higher than the WHO standard. Few studies have investigated the characteristics, sources, and control strategies for the whole country. We perform year-long WRF-Chem and WRF-CMAQ simulations over entire India to understand the key physical and chemical processes contributing to the severe haze pollution and their seasonality. We evaluate the model performance using surface meteorology and speciated PM, as well as AOD and precursor gases from satellite. We find WRF-Chem is comparable with surface PM measurements for less-haze days. The modified WRF-CMAQ with newly added heterogeneous reactions is better to reproduce extreme polluted conditions in winter time. Meteorological biases can also influence the chemistry and exacerbate the PM biases in the models. The aerosol radiation feedbacks to the surface PM concentration account for about 10% of PM variations.