PM 2.5 pollution exceeding Indian standard over a semi-urban region at eastern IGP: Chemistry, meteorological impact, and long-range transport

A year-long study (January-December 2019) on the chemical characterization and meteorological impact on PM was conducted over a semi-urban station, Shyamnagar, in the easternmost part of the Indo-Gangetic Plains (IGP). PM concentrations (Mean = 81.69 ± 66.27 μgm ; 7.10-272.74 μgm ), the total carbonaceous aerosols (TCA) (Mean = 22.85 ± 24.95 μgm ; 0.77-102.97 μgm ) along with differential carbonaceous components like organic carbon (OC) (Mean = 11.28 ± 12.48 μgm ; 0.48-53.01 μgm ) and elemental carbon (EC) (Mean = 4.83 ± 5.28 μgm ; 0.1-22.13 μgm ) exhibited prominent seasonal variability with the highest concentrations during winter, followed by post-monsoon, pre-monsoon and lowest during monsoon. A similar seasonal variation was observed for the total water-soluble ionic species (Mean = 31.91 ± 20.12 μgm ; 0.1-126.73 μgm ). We observed that under the least favorable conditions (low ventilation coefficient), high PM pollution (exceeding Indian standard) was associated with a high increase in secondary components of PM . Eastern, central and western parts of IGP, as well as Nepal, were the major long-distant source regions whereas the northern part of West Bengal and parts of Bangladesh were the major regional source region for high PM pollution over Shyamnagar. The ratios like char-EC/soot-EC, non-sea-K /EC and non-sea-SO /EC strongly indicated the dominance of fossil fuel burning over biomass burning. Compared with other studies, we observed that the PM pollution over this semi-urban region was comparable (and even higher in some cases) with other parts of IGP. The high exceedance of PM over the Indian standard in Shyamnagar strongly demands an immediate initiation of systematic and regular based air pollution monitoring over semi-urban/non-urban regions in India, especially IGP, in addition to the polluted cities.