Decadal analysis of black carbon aerosols over the central Indo-Gangetic Plain: trends, source regions, and policy impact

Abstract

Light-absorbing carbonaceous aerosols majorly contribute to regional air pollution over the Indo-Gangetic Plain (IGP). This study examines a decade-long (2013−2023) measurement of in-situ Black Carbon (BC) concentrations, along with satellite-derived Absorbing Aerosol Index (AAI) and Fire Counts (FC), to analyse seasonal variations, trends and identify potential sources at a central IGP site. The analysis showed notable seasonal variations in BC, ranging from 0.11 to 62 μg m−3, with winter (W) peaking at 16 ± 10 μg m−3 and monsoon (M) at a low of 4 ± 2 μg m−3. Biomass burning (BB) contributed the most (32 ± 13 %) during the post-monsoon (PoM). The trend analysis showed a statistically significant (SS) decreasing trend in BC mass concentration of 0.57 μg m−3y−1 (6.7 % y−1). The SS decreasing rate observed in BC from fossil fuels (BCff) is 0.51 μg m−3y−1 and in BC from biomass burning (BCbb) is 0.06 μg m−3y−1. In comparison, the meteorological and satellite parameters show statistically insignificant change, pointing towards the effectiveness of policies such as Pradhan Mantri Ujjwala Yojana (PMUY), National Clean Air Programme (NCAP), implications of Bharat Stage (BS) norms, emission control measures, and shifts towards cleaner fuels. A negligible fall in BCbb results in its increasing contribution (1.17 % y−1) towards BC, suggesting the need of aimed measures to deal with BB practices. During the PoM season, a peak in the high compensation parameter (K) of 0.00896 is observed, indicating freshly emitted BC aerosols typically associated with BB activities and fossil fuels. A high-frequency peak at a low K value (−0.00312) is observed during W only, indicating the presence of aged aerosols with enhanced scattering properties. Source apportionment analysis shows the dominant contribution to BC levels in the central IGP is mainly from the western part of the IGP.