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Long-term observation of black carbon aerosols at an urban location over the central Indo-Gangetic Plain, South Asia

Sambhawika Srivastava, Manish Kumar, Ram S. Singh, Birendra N. Rai, Rajesh K. Mall, Tirthankar Banerjee

Abstract

The first ever long-term measurement of black carbon (BC) aerosols over an urban location at the central Indo-Gangetic Plain (IGP) is presented. Both short- and long-term variations in BC during the period 2009-2013 are discussed with specific emphasis on variation in BC sources, meteorology, trend and possible transport pathways across the IGP. High BC mass loading was noted with a 5-yr composite mean (± SD) of 11.8 (± 8.6) µg m–3, having strong and consistent seasonal variations (median: 8.8; range: 1.4-48.0 µg m–3). Winter (21.5 ± 9.9µ gm–3) and post-monsoon (17.4 ± 10.2 µg m–3) specific rises in BC mass were consistent with the increase in household emissions, and from agricultural residue burning. The BC mass concentration was mostly influenced by local sources, while sudden change in BC was consistent with the change in Delta-C, indicating emissions primarily from biomass burning. Beside sources, atmospheric boundary layer height was noted to considerably influence short-term variations in BC concentration. A statistically significant monotonic increasing trend in BC concentration (0.9 µg m–3 yr–1) was computed along with its 95% uncertainty bounds (0.38-1.52 µ gm–3 yr–1). Increase in BC concentration was consistent with a rise in BC sources across the IGP and over India. Furthermore, clear evidence of local and regional scale transport of BC aerosols was found using the particle Lagrangian model.

Keywords

Black carbon; South Asia; Mann-Kendall test; IGP; biomass burning; Delta-C; atmospheric boundary layer

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