Absorption properties of black carbon aerosols over environmentally distinct locations in south-western India: Temporal, spectral characterization and source apportionment

Abstract

The near-simultaneous measurements of wavelength dependent light absorption properties of black carbon (BC) aerosols employing the seven-channel, model AE-33 Aethalometers are carried out from the campuses of Ahmednagar College, Ahmednagar (AC-Ahmednagar) and Indian Institute of Tropical Meteorology, Pune (IITM-Pashan) from December 2015 to December 2016. Analysis brings out statistically significant higher values of BC absorption coefficient [σabs,880 nm (BC), Mm−1] (hence BC mass concentration) at site AC-Ahmednagar (annual mean = 99.95 ± 79.8 Mm−1) as compared to those at site IITM-Pashan (annual mean = 47.19 ± 59.9 Mm−1). The seasonal mean values of σabs,880 nm (BC) illustrate conspicuous intra-seasonal variability at both the locations. This variability seems to be influenced by the seasonal nature and strengths of BC emission sources, local meteorology, dynamics in atmospheric boundary layer (ABL) and modulation in advection pathways. The absorption Ångström exponent (AAE) analysis reveals that there exists a predominant contribution to the total BC by fossil fuel emission enriched mixed carbonaceous aerosols as well as freshly emitted fossil fuel burning BC aerosols at site AC-Ahmednagar while at site IITM-Pashan the major contribution to the total BC appears to come from fossil fuel/biomass emission enriched mixed carbonaceous aerosols. The source apportionment of BC mass depicts that the fractional contributions of BC_FF to BC mass dominate throughout the year at both observing locations. Seasonal variability of BC_BB fraction of BC at both locations is found to be complimentary to the seasonal variability of BC_FF fraction of BC at respective sites.