Seasonal variability and source apportionment of black carbon over a rural high-altitude and an urban site in western India

Abstract

Black carbon (BC) mass concentration observations were carried out using Aethalometer (AE-33) at an urban site Pune and at a high altitude forest site Mahabaleshwar during April 2018 to February 2019. The annual averaged BC mass concentration over Pune was observed to be ~2.8 times higher than Mahabaleshwar. Daily, seasonal and diurnal variations of BC over these two different environments were compared. The effect of meteorological parameters on the BC was also evaluated. Planetary boundary layer (PBL) plays a pivotal role in diluting the atmospheric pollutant BC during daytime at Pune, whereas, contribution of combustion sources mostly dominated over PBL dilution at Mahabaleshwar. Higher wind speed regime also tends to dilute the atmosphere whereas higher BC concentration was observed during RH condition depicting the significance of low dispersion under these conditions. The contribution of different sources namely biomass burning (BB) and fossil fuel (FF), wavelength dependent source apportionment study was also evaluated. Traffic emission contributed 72%–75% of the BC loading at Mahabaleshwar, whereas at Pune it was estimated to be 82%–94% during all the seasons indicating BB contributed more at Mahabaleshwar. Cluster analysis and concentration weighted trajectory (CWT) analysis were also performed to visualize the importance of regional transport for both the locations. The study confers the significance of regional transport in addition to local emissions over both the sites.