Meteorological modulation of ambient air quality in Delhi and Lahore during the November 2024 haze event

Abstract

Abstract The Indo-Gangetic Plain in South Asia frequently experiences severe haze during the post-monsoon season. The November 2024 haze event recorded the highest daily PM 2.5 concentrations in Delhi (696 µg/m³) and Lahore (621 µg/m³) over the past 5 years. These elevated PM 2.5 concentrations coincided with a prolonged period of regional-scale atmospheric stagnation and a shift in peak fire activity from the afternoon to the evening. Here, we show that both cities had elevated pollutant concentrations with correlations between PM 2.5 and planetary boundary layer height, lower-tropospheric stability, atmospheric heat deficit, relative humidity, and fire radiative power, consistent with accumulation of emissions from multiple sources, including regional biomass-burning emissions, under stagnant atmospheric conditions. We also highlight that positive geopotential height anomalies and the mechanism of anticyclonic stagnation and weak winds favored a high-pressure system, suppressing turbulent ventilation and accumulating pollution in the lower troposphere. Furthermore, air mass back trajectories overlapped the stubble-burning region ,and higher evening fire counts observed by a geostationary satellite emphasize the likely role of increased evening fire activity alongside other local and regional emissions in elevated air pollution concentrations. These results demonstrate that local and synoptic meteorology strongly aggravates haze events, suggesting emission control strategies should be guided by meteorological forecasts across regional airsheds.