Investigations of black carbon aerosol sources and strengths over a rural-valley location in Haryana, India

Observations of equivalent Black Carbon (eBC) aerosols were carried out at Panchgaon, a rural site in Haryana, nestled amidst the Aravali hillocks (285 m AMSL) in northwest India. These measurements were carried out using a next-generation seven-wavelength Aethalometer (AE33) from January 2020 through December 2022. The Aethalometer model was used to quantify the relative contributions of fossil fuel (eBCff) and biomass burning (eBCbb) to total eBC, revealing the greater contribution of these sources consistent with regional emission characteristics. These stronger absorbers of solar radiation exhibit a diurnal pattern, with the highest values in the morning, evening hours and minimum values around afternoon hours. The annual mean concentrations of eBC, eBCff, and eBCbb are found to be 4.06 ± 2.15 μg/m3, 3.10 ± 2.40 μg/m3, and 1.42 ± 1.19 μg/m3, respectively, during the study period. Both eBCff and eBCbb sources show maximum value in winter (eBCff: 4.19 μg/m3, eBCbb: 2.51 μg/m3) as compared to summer and monsoon months. This may be attributed to increased biomass burning in the surrounding area, as it is primarily a rural site. During winter, the site experiences lower atmospheric temperatures and wind speeds, due to the pollution getting trapped near the surface due to lower boundary layer height, followed by summer (eBCff: 3.60 μg/m3, eBCbb: 1.87 μg/m3) and post-monsoon (eBCff: 2.30 μg/m3, eBCbb: 1.08 μg/m3). The lowest values of eBCff (1.90 μg/m3) and eBCbb (0.52 μg/m3), exhibited in monsoon, could be due to cloud- and rain-scavenging effects. eBCff accounts for the majority of the contribution, with an average fraction of 68% at 880 nm, while biomass burning contributes the remaining 32%. The average eBCff/eBCbb ratio is 3.02 ± 3.80 at 880 nm. These findings provide valuable insights for designing targeted control emission strategies in semi-urban to rural regions, with implications for improving air quality and addressing regional climate impacts.