Aerosol black carbon characteristics over a high-altitude Western Ghats location in Southern India

Aerosol black carbon (BC) mass concentrations were continuously monitored over a period of 2 years (April 2010 to May 2012) from a high-altitude location Ooty in the Nilgiris Mountain range in southern India to characterize the distinct nature of absorbing aerosols and their seasonality. Despite being remote and sparsely inhabited, BC concentrations showed significant seasonality with higher values (~ 0.96 plus or minus 0.35 mu g m-3) in summer (March to May), attributed to increased vertical transport of effluents in the upwind valley regions, which might have been confined to the surrounding valley regions within the very shallow winter boundary layer. The local atmospheric boundary layer (ABL) influence in summer was further modulated by the long-range transported aerosols from the eastern locations of Ooty. During monsoon (June-August), the concentrations were far reduced (~ 0.23 plus or minus 0.06 mu g m-3) due to intense precipitation. Diurnal variations were found conspicuous mainly during summer season associated with local ABL. The spectral absorption coefficients ( alpha abs) depicted, in general, flatter distribution (mostly < 1.0 for more than 85% of daily mean values), suggesting the relative dominance of fossil fuel combustion, though showed marginal seasonal change with higher values of alpha abs in summer.