Black carbon aerosols over a semi-arid rain shadow location in Peninsular India: Temporal variability and sources

Continuous measurements of absorbing carbonaceous aerosol termed as black carbon (BC) have been carried out during April 2017 to March 2018 over Solapur, a semi-arid, rain shadow location in Peninsular India using a multi-wavelength Aethalometer (AE-33). Statistically significant higher values of BC were observed during the dry period (December–May, mean BC 4.3±1.2 µg m–3) as compared to the wet period (June–October, mean BC 1.0 ± 0.15 µg m–3). Hourly variation depicted an almost similar pattern in both wet and dry periods with a dominant morning peak followed by afternoon low and then a heightened plateau during the evening to midnight hours. The absorbing Angstrom exponent (AAE) value was 1.36 ± 0.16 and 1.10 ± 0.22, respectively, during dry and wet periods with an annual mean of 1.22 ± 0.23. The source apportionment of BC using the Aethalometer model depicts the dominance of fossil fuel burning throughout the year especially high during the wet period (89±11% to total BC) whereas biomass burning contributed significantly during the dry period (30±14% to total BC). The observed temporal variation of BC was mainly due to the varying strength of BC emission sources and changes in local meteorological parameters. In addition, long-range transport from other regions might have also contributed during certain periods as seen from the cluster and concentration weighted trajectory (CWT) analysis.