Understanding meteorological factors influencing heavy air pollution in Guwahati, India

Guwahati, Assam's largest city and the gateway to Northeast India faces rapid urbanization and increasing pollution. Although heavy air pollution has been frequent in recent decades, the exact reason behind this is still uncertain. During the study period from 2021 to 2023, we identified eight instances of heavy pollution events across the region, seven of which are aligned with a high-pressure system and influenced by westerly airflow at 700 hPa. Apart from that, temperature inversion, low boundary layer height, and low horizontal wind speeds in the lower troposphere help confine pollution, resulting in insufficient mixing and dispersion of pollutants in the atmosphere, which favors the development of heavy air pollution episodes. We investigated the impact of local and regional emissions on PM10 and PM 2.5 concentrations over Guwahati City using the regional Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). Our finding revealed that regional transport significantly contributes to PM10 (57.3 %-75.5 %) and PM 2.5 (56.9 %-73.5 %) levels, highlighting the predominance of regionally transported pollutants. During high pollution days, local emissions increase due to stagnant air, limited dispersion from high-pressure systems, and temperature inversions, trapping pollutants in the region. This research offers valuable scientific knowledge to anticipate heavy air pollution episodes in Guwahati.