Indo-Gangetic Plain experiences higher aerosol pollution than North China Plain despite lower emissions.

Abstract

We investigate the spatiotemporal dynamics of aerosol pollution in the Indo-Gangetic Plain (IGP) and the North China Plain (NCP), two of the world's most populated regions, against their anthropogenic emissions. Utilizing CAMS EAC4 reanalysis, CAMS-GLOB-ANT emission inventories, and ERA5 meteorological data for the year 2019, we analyze the seasonally changing relationship between PM-forming emissions and ambient PM_2.5 concentrations. We find a significant disparity: despite the NCP emitting 65% more total anthropogenic particulates and precursors annually (28,860 KT vs. 17,464 KT), the IGP suffers higher annual average PM_2.5 concentrations (123.6 vs. 113.2 µg/m3). Temporal and episode analyses reveal that large swathes of both regions are engulfed in polluted air during much of the year, with some respite during the summer and monsoon seasons. The NCP, with lower annual average PM_2.5, records more total "bad air quality" days (251 vs. 238), while the IGP is characterized by fewer but more prolonged episodes, with extreme stagnation events in the Delhi region lasting up to 170 consecutive days. To quantify the regional contrast in atmospheric response, we introduce the "Pollution Forming Efficiency" (PFE) metric. Our results show that during winter, the IGP's PFE is nearly double that of the NCP, meaning that the IGP atmosphere converts unit emissions into ambient concentrations far more effectively. We identify regional meteorology as the primary driver; the IGP is characterized by stagnant winds (< 6 km/h) and a shallow planetary boundary layer (< 300 m) leading to a consistently lower ventilation coefficient that inhibits vertical mixing and dispersion of pollution. Ultimately, our findings reveal that there is an inherent meteorological vulnerability to the IGP, and therefore, any economic growth strategy in this region must account for its limited carrying capacity. Recognizing that the IGP atmosphere uniquely amplifies the health impact of every kilogram emitted is the first step toward securing a breathable future for the more than one billion people who call these plains home.