Assessment of Winter-Time Carbon Content in PM10 Over a High-Altitude Atmosphere of Eastern Himalaya
摘要
The carbon content [organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), total carbonaceous matter (TCM), primary organic carbon (POC) and secondary organic carbon (SOC)] of respirable particulate matter (PM10) was estimated at the eastern Himalayan region (Darjeeling) of India during 4 consecutive winter seasons (W-I: December 2018–February 2019; W-II: December 2019–February 2020; W-III: December 2020–February 2021; and W-IV: December 2021–February 2022) to examine their concentration, sources and environmental impact. During four consecutive winter seasons, the mean concentrations of PM10, OC, EC, WSOC, and TCM were estimated as 60 ± 20 µg m−3, 6.0 ± 1.9 µg m−3, 2.7 ± 1.1 µg m−3, 3.4 ± 1.3 µg m−3, and 12.5 ± 4.1 µg m−3, respectively. The overall mean carbonaceous aerosols (CAs) mass concentration of PM10 was estimated to be ~ 21% of PM10 during winters [W-I (CAs: 23.9%), W-II (CAs: 19.7%), W-III (CAs: 19.6%), and W-IV (CAs: 20.3%)]. Results showed the non-significant variations (at p ≤ 0.05) in mass concentrations of PM10, OC, EC, TCM, POC, and SOC among all winters season. The relationship between OC, EC, & WSOC and their weight ratios (OC/EC, OC/WSOC, EC/TC) suggested that fossil fuel combustion [(FFC; including vehicular fuel combustion (VFC)] and biomass burning (BB) are the major sources of CAs at Darjeeling. In the present case, the mean effective carbon ratio (ECR) is computed as 0.33 (range: 0.04–0.76; ECR < 1) which demonstrates the abundance of POC species more than the SOC and indicates the warming effects of CAs over the study site. The air mass backward trajectory analysis indicates that CAs approaching to the sampling site of Darjeeling primarily originated from the Nepal, Bhutan, Tibet, the IGP, the Thar Desert and Pakistan.