Seasonal characteristics of black carbon aerosols over a high altitude station in Southwest India

Black carbon (BC) aerosol mass concentrations were measured using an Aethalometer at high altitude station Sinhagad, a rural location in south-west India, in the pre-monsoon and post-monsoon seasons during 2009–10. Mean BC concentration was about 67% less during pre-monsoon than that during post-monsoon. During post-monsoon, the surface boundary layer is generally shallow resulting in the trapping of pollutants in a lesser volume near the surface which lead to higher BC concentrations than of pre-monsoon which experiences high convective activity and thereby dispersion of aerosols near the surface. Diurnal variation of BC during pre-monsoon was attributed to the changes in the local boundary layer as well as to the certain anthropogenic activities near the sampling site. BC aerosol mass concentration showed good correlation with temperature gradient and relative humidity in pre-monsoon. However in post-monsoon, a weak correlation was observed with temperature gradient whereas with relative humidity, a good correlation was observed during night hours only. The wind speed and direction using NCEP/NCAR reanalysis data showed a possible transport from Pune city as well as from N/NE Indian regions during post-monsoon. BC also showed good correlation with other anthropogenic components of aerosols like NssSO4, NssK, NO3, and NH4; indicating a possible common source for them.