Drivers of PM2.5Episodes and Exceedance in India: A Synthesis From the COALESCE Network

Emission sources influencing high particulate air pollution levels and related mortality in India have been studied earlier on country‐wide and sub‐national scales. Here, we use novel data sets of emissions (for 2019) and observations created under the Carbonaceous Aerosol Emissions, Source Apportionment, and Climate Impacts network in India (Venkataraman et al., 2020, https://doi.org/10.1175/bams‐d‐19‐0030.1) in WRF‐Chem simulations to evaluate drivers of high PM2.5levels during episodes and in airsheds with different pollution levels. We identify airsheds in “extreme” (110–140 μg/m3), “severe” (80–110 μg/m3) and “significant” (40–80 μg/m3) exceedance of the Indian annual ambient air quality standard (National Ambient Air Quality Standards [NAAQS]) of 40 μg/m3for PM2.5. We find that primary organic matter and anthropogenic mineral matter (largely coal fly‐ash) drive high PM2.5levels, both annually and during high PM2.5episodes. PM2.5episodes are driven by organic aerosol in north India (Mohali) in wintertime but are additionally influenced by mineral matter and secondary inorganics in central (Bhopal), south India (Mysuru) and eastern India (Shyamnagar). Across airsheds in exceedance of the NAAQS and during high PM2.5episodes, primary PM2.5emissions arise largely from the residential sector (50%–75%). Formal sector emissions (industry, thermal power and transport; 40%–55%) drive airshed and episode scale PM2.5exceedance in northern and eastern India. Agricultural residue burning emissions predominate (50%–75%) on episode scales, both in northern and central India, but not on annual scales. Interestingly, residential sector emissions strongly influence (60%–90%) airsheds in compliance with the NAAQS (annual mean PM2.5< 40 μg/m3), implying the need for modern residential energy transitions for the reduction of ambient air pollution across India. India faces high levels of air pollution, particularly that of breathable pollution particles, exposure to which leads to large public health impacts, in terms of reduced life spans and more frequent illness. In this work we ask questions about which pollutant species and which emission sources largely affect time periods (or episodes) and regions (or airsheds) where high pollution occurs. We find that organic matter from biomass combustion and mineral matter from coal combustion, are associated with high pollution levels. Biomass combustion is related to residential cooking with fuelwood and crop residue stalks traditional stoves, while coal combustion arises in coal‐fired power plants and industry. While agricultural stubble burning has been highlighted in the media, it affects high pollution episodes in some regions, but is less important on annual scales. Importantly, large residential emissions arise both in cleaner and polluted regions across India, making modern residential energy transitions key to reducing air pollution in India. Primary organic matter and anthropogenic mineral matter (coal fly‐ash) drive both high annual and episodic PM2.5levels, across IndiaAgricultural residue burning emissions predominate on episode scales, both in northern and central India, but not on annual scalesResidential energy transitions key to air pollution mitigation as residential sector emissions dominate both cleaner and polluted airsheds Primary organic matter and anthropogenic mineral matter (coal fly‐ash) drive both high annual and episodic PM2.5levels, across India Agricultural residue burning emissions predominate on episode scales, both in northern and central India, but not on annual scales Residential energy transitions key to air pollution mitigation as residential sector emissions dominate both cleaner and polluted airsheds