Relationship between black carbon and associated optical, physical and radiative properties of aerosols over two contrasting environments

The first simultaneous aethalometer and solar radiometer measurements of black carbon (BC) mass concentration (surface-level) and aerosol optical, microphysical and radiative parameters (columnar) have been made during 2005–2011 over two contrasting experimental sites, one representing background rural environment (Sinhagad) and the other surrounded by urban environment (Pune) in the south-west India. The long-term diurnal cycle of BC aerosols over both sites exhibited a strong peak during daytime and a weaker plateau around evening–midnight hours, implying the influence of anthropogenic emissions as well as changes in planetary boundary layer (PBL). The multi-year seasonal mean variation in BC concentration shows the highest during winter and lowest during monsoon seasons, which is found to be inversely related to the variations in single scattering albedo (SSA). Moreover, the BC variations were found to be strongly associated with greater values of Angstrom exponent (α), indicating that the observed BC involves abundance of fine-mode aerosol fraction. The higher concentrations of BC during winter and lower concentrations during pre-monsoon over both Pune and Sinhagad are noticed to be closely linked with aerosol optical depth, revealing significant contribution of BC to the composite aerosol over both the regions. The columnar AOD and Angstrom exponent also showed relatively greater optical depth and α values during winter as compared to pre-monsoon season over both sites.