Seasonal variation of PM2.5 in the central Indo-Gangetic Plain (Patna) of India: chemical characterization and source assessment

Abstract

While characteristics, sources, and formation process of PM2.5 have been widely reported, only a few studies discussed PM2.5 in the Indian subcontinent, specifically in a densely populated city, like Patna. In this study, we investigated the chemical composition and source of PM2.5 in the central Indo-Gangetic Plain of India (Patna), during January–December, 2018. Principal component analysis (PCA) and air mass back trajectory were performed to mark the sources of PM2.5. The result showed that the average annual PM2.5 level in Patna (172 µg/m3) was about 4 times greater than the annual limit (40 µg/m3) set by national ambient air quality standard of India, indicating the dangerous level. Overall, the highest level of water-soluble inorganic ions (ΣWSIIs) was measured in winter, followed by autumn, and ranged from 2 to 60 µg/m3 (median 16 µg/m3) and 3 to 47 µg/m3 (median 14 µg/m3), respectively. NH4+, SO42−, and NO3− were the most abundant ions in PM2.5 and accounted for 38–51%, 21–28%, and 8–20% of ΣWSIIs, respectively. The PCA analysis indicated primary emission from mixed source (street dust, coal combustion, biomass burning, vehicular emission, and industrial emissions) and secondary formation from coal combustion are the essential source of air pollution in Patna. The air mass back trajectory analysis revealed that most of the air mass at Patna arrives mainly from westerly/northwesterly direction originating from Pakistan and Afghanistan in winter/autumn, while westerly/southwesterly winds originating from Arabian Sea and crossing through Bay of Bengal impacted air quality in summer/rainy season.