Seasonal Transport Pathway and Sources of Carbonaceous Aerosols at an Urban Site of Eastern Himalaya

Autor: Arin Chatterjee, Sauryadeep Mukherjee, Akansha Rai, Sudhir Kumar Sharma, Tuhin Kumar Mandal, R.K. Kotnala, Abhinandan Ghosh, Nikki Choudhary
Rok vydání: 2021
Předmět:
Zdroj: Aerosol Science and Engineering. 5:318-343
ISSN: 2510-3768
2510-375X
DOI: 10.1007/s41810-021-00106-5
Popis: In this study, we examined the seasonal transport pathways of carbonaceous species [Organic Carbon (OC), Elemental Carbon (EC), Water-Soluble Organic Carbon (WSOC), Primary Organic Carbon (POC), Secondary Organic Carbon (SOC), and Total Carbonaceous Aerosols (TCAs)] of PM2.5 and PM10 over a semi-urban high-altitude site of Darjeeling (27.041oN, 88.266oE, 2200 m above mean sea level (amsl); an eastern Himalayan region), India during August 2018–July 2019. The annual average concentrations of PM2.5 and PM10 were 37 ± 12 µg m−3 and 55 ± 18 µg m−3, respectively that was within but quite close to the threshold limit of National Ambient Air Quality Standards (NAAQS) (annual 60 μg m−3 for PM10; and 40 μg m−3 for PM2.5). The seasonal average concentration of OC in PM2.5 was highest in pre-monsoon (4.2 ± 1.7 µg m−3) > post-monsoon (4.0 ± 1.6 µg m−3) > winter (3.3 ± 1.5 µg m−3) > monsoon (2.2 ± 0.9 µg m−3) whereas OC in PM10, in the order of highest in post-monsoon (5.9 ± 2.4 µg m−3) > winter (5.4 ± 2.0 µg m−3) > pre-monsoon (5.2 ± 2.1 µg m−3) > monsoon (3.6 ± 0.9 µg m−3). Similar seasonal variation in case of EC in both PM2.5 (winter 1.8 ± 0.8 µg m−3; pre-monsoon 2.2 ± 0.9 µg m−3; monsoon 1.2 ± 0.4 µg m−3; post-monsoon 2.2 ± 1.1 µg m−3) and PM10 (winter 2.7 ± 1.0 µg m−3; pre-monsoon 3.0 ± 1.1 µg m−3; monsoon 1.2 ± 0.4 µg m−3; post-monsoon 1.9 ± 1.2 µg m−3) were observed during the study period. Based on different altitudes (100, 500, 1000 m), the seasonal backward trajectory and its concentration-weighted trajectory (CWT) analysis reveal the local, Indo-Gangetic Plain (IGP), the Thar desert, semi-arid, central highlands, Nepal, and the Bay of Bengal (BoB) as the common pollutant transporting regions to the observational site of Darjeeling. Also, its cluster analysis at 500 m above ground level (AGL) indicates that air mass originates mainly from 3 sides [western region, Thar desert (17.6%); north-western region, Nepal (45.1%); southern region, Bangladesh (37.3%)] during the study. Due to high tourist influx in pre-monsoon (peak tourist season), the maximum contribution of carbonaceous aerosols was mainly from the vehicular sources, coal combustion, transboundary pollutants, biomass burning in the IGP region, and the formation of secondary organic aerosols (SOA). Besides, active Terra and Aqua MODIS fire and thermal anomalies (≥ 80 per cent) indicated the maximum prevalence of fire spots during pre-monsoon across India (except the Thar desert) followed by post-monsoon (due to crop-residue burning) in Punjab and Haryana.
Databáze: OpenAIRE
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