CARBONACEOUS AEROSOLS OVER INDO-GANGETIC PLAIN IN INDIA : SPATIAL AND TEMPORAL VERIATION AND POTENTIAL SOURCE REGIONS

Abstract

Indo-Gangetic plain - India’s most densely populated area comprises some of the world’s most smog-plagued cities. The area witnesses the worst air pollution episodes each year burdened by PM2.5 of which the major section is carbonaceous aerosols. Hence, in this study, the BC and OC surface mass concentration trends of 6 highly polluted IGP cities are analyzed for temporal variations, and the assertive role of meteorology and long-range transfer of carbonaceous aerosols has been studied. The reanalysis data from Modern-Era Retrospective Analysis for Research and Applications version-2 (MERRA-2), for BC and OC from January 2019 to December 2021 for 6 cities have been investigated for seasonal, monthly, and yearly variations. The 5-day air back trajectory has been studied using the Hybrid Single-Particle Lagrangian Integrated Trajectory Model (HYSPLIT) backward trajectory clustering and concentration weighted trajectory (CWT) analysis for identifying the regional transport of aerosols. Correlation analysis was performed for carbonaceous species (BC & OC), PM2.5, gaseous air pollutants, and meteorological conditions for the study areas. The annual average BC and OC were found to be highest for Muzaffarpur, Bihar. The monthly means for BC, OC, and OC/BC for IGP ranged between 0.94 to 10.05 µgm-3, 3.49 to 48.74 µgm-3, and 3.56 and 11.11 respectively. The concentrations were observed to peak in the winter months followed by post monsoon and summers with the least values exhibited in monsoon throughout the IGP except for Guwahati. Guwahati displayed a peculiar pattern with a peak observed in March of every year. OC/BC ratio above 4 was reported for all locations indicating the burning of fossil fuels, biomass, dust storms, transportation, and industrial activities as the major polluters. For all locations, OC and BC were positively and significantly correlated (>0.95) indicating common emission sources. Carbonaceous aerosols displayed a moderate to strong correlation with PM2.5 and an inverse correlation with Wind Speed, Relative Humidity, and Ambient Temperature. v

Based on the cluster and CWT analysis, IGP itself was identified as a major contributor to BC and OC loads. Long-range transportation of aerosols from Myanmar; Bangladesh; Tibet; Yunnan China; the Arabian Sea, Laccadive Sea, and the Bay of Bengal was observed for most of the locations during the monsoon season. Moreover, the Sindh and Punjab regions of Pakistan were also contributing.