Separating emission and meteorological drivers of mid-21st-century air quality changes in India based on multiyear global-regional chemistry-climate simulations

Many Indian metropolitan areas currently suffer from severe air pollution such as PM2.5, which might continue into future decades, dependent on the trends in emission growth and regional climate. Based on a multiyear Nested Regional Climate Model coupled with Chemistry simulation, we developed a daily index (Hazy Weather Index for India, HWII) to characterize the meteorology-pollution relationship over three heavily polluted cities (Delhi, Kolkata, and Mumbai) and Indo-Gangetic Plain. HWII consists of near-surface (10 m) zonal wind (U10) and temperature at 200 hPa (T200) over the northwestern Indian Ocean, and local planetary boundary layer height. The simulated PM2.5 levels during the Historical Period (1997-2004) exhibit robust negative correlation with the HWII. The negative correlation captures day-to-day covariability of surface PM2.5 and meteorology, highlighting the role of monsoon-related large-scale circulation in redistributing locally emitted pollutants. More importantly, two future (2046-2054) simulations with regional warming under the Representative Concentration Pathway 6.0 and 8.5 were analyzed. The future changes in HWII and the three predictive meteorological variables work in favor of a stronger pollution horizontal dispersion and vertical ventilation and thus could lead to a reduction of PM2.5 level by 7%. The meteorology-driven reduction in PM2.5, however, is overwhelmed by the projected growth in anthropogenic emission (especially under Representative Concentration Pathway 8.5 emission by 31%). Our results are contrary to previous studies over other regions (e.g., China) where future climate change might contribute to PM2.5 increase.