Aerosol loading in the atmospheric boundary layer at Trivandrum coast and in the adjoining oceanic environments during the FFP and IFP of the INDOEX

摘要

During the First Field Phase (FFP-98) and the Intense Field Phase (IFP-99) of the INDOEX, characteristics of atmospheric aerosols near the surface and in the atmospheric boundary layer have been studied at Trivandrum using a high volume sampler, a low pressure impactor and a CW lidar, The data obtained from these measurements along with the mass concentrations measured on cruises are used to study the spatial distribution of atmospheric aerosols and the advection of continental aerosols in the oceanic environments. During IFP-99 a significant increase in aerosol loading was observed near the surface and in the atmospheric boundary layer. The daytime mass concentrations (m) measured at Trivandrum are comparable with the measurements conducted on cruise in the adjoining oceanic regions. The nighttime aerosol mass concentrations at Trivandrum are relatively high in January. The day-night contrast in decreases during March. A large build-up in m was observed at Trivandrum associated with the changes in circulation pattern (land breeze-sea breeze), This is attributed to horizontal convergence. The aerosol size distribution measured using the impactor, in general, is trimodal, In February and March the sub-micron mode shifts towards smaller size regime (< 0.02 mum), The large particle mode (between 0.1 and 1 mum) is rather broad and gets split into two at times. The gross form of near surface aerosol size distribution can be approximated to a power law, with the size index in the range 3.7 to 4.4. This size index shows a decrease during IFP-99 period, indicative of a relative increase in larger size particles. The mixing region aerosol optical depth also is relatively high during IFP-99, The mass concentration measured along the West Coast on the cruise shows an increase during IFP-99. Along the coast, as the ship sails from Coa towards south, the aerosol mass concentration first decreases and then increases as the ship approaches Cochin, This increased concentration remains steady up to the southern tip of the Indian peninsula. A significant decrease in m was observed in the ITCZ region, The aerosol concentration south of ITCZ was less than that in the North (in the Arabian Sea region). An increased concentration of aerosols was observed in the mid-Arabian Sea oceanic environments, which was attributed to advecting aerosols due West and North. [References: 21]