Aerosol optical properties and composition over a table top complex mining area in a monsoon trough region

Aerosol physiochemical properties over a varied mining plateau region at the eastern end of a monsoon trough are reported for the first time and analyzed at different time scales. Aerosol optical depth (single scattering albedo, SSA) is found to be 0.49 (0.9) in pre-monsoon, 0.4 (0.94) in monsoon, 0.46 (0.92) in post-monsoon, and 0.36 (0.89) in winter, with an annual mean of 0.43 (0.91). The volume-size distribution is tri-modal, with 0.02 (ultra-fine), 0.2 (accumulation) and 7 (coarse) µm, but with seasonal signatures. The angstrom exponent (AE) varies along with the AOD, especially in winter, although they are inversely related to each other during monsoons; the increase in size may be due to the effect of humidity. AODbc varies between 13.4%–4.7% of the total aerosols, with the highest contribution in March, when forest burning in the north east is at its peak. BC is the lowest in July, the mid monsoon month with the minimum biomass burning and brick-kiln activities. It is likely that the interactions of various minerals and intermittent rains help keep the aerosol size in a mixed state with regard to the relation between AE and AOD, although more work is needed to confirm this. The chemical composition of aerosols is derived from an aerosol chemical model based on the measured amount of black carbon and the assumed components