Abstract
BackgroundThe loading of atmospheric particulate matter (aerosol) in the eastern Himalaya is mainly regulated by the locally generated anthropogenic aerosols from the biomass burning and by the aerosols transported from the distance sources. These different types of aerosol loading not only affect the aerosol chemistry but also produce consequent signature on the radiative properties of aerosol.Methodology/Principal FindingsAn extensive study has been made to study the seasonal variations in aerosol components of fine and coarse mode aerosols and black carbon along with the simultaneous measurements of aerosol optical depth on clear sky days over Darjeeling, a high altitude station (2200 masl) at eastern Himalayas during the year 2008. We observed a heavy loading of fine mode dust component (Ca2+) during pre-monsoon (Apr – May) which was higher by 162% than its annual mean whereas during winter (Dec – Feb), the loading of anthropogenic aerosol components mainly from biomass burning (fine mode SO4 2− and black carbon) were higher (76% for black carbon and 96% for fine mode SO4 2−) from their annual means. These high increases in dust aerosols during pre-monsoon and anthropogenic aerosols during winter enhanced the aerosol optical depth by 25 and 40%, respectively. We observed that for every 1% increase in anthropogenic aerosols, AOD increased by 0.55% during winter whereas for every 1% increase in dust aerosols, AOD increased by 0.46% during pre-monsoon.Conclusion/SignificanceThe natural dust transport process (during pre-monsoon) plays as important a role in the radiation effects as the anthropogenic biomass burning (during winter) and their differential effects (rate of increase of the AOD with that of the aerosol concentration) are also very similar. This should be taken into account in proper modeling of the atmospheric environment over eastern Himalayas.
Highlights
The increase in the loading of atmospheric aerosols over the Himalaya is a matter of concern, since most of the glaciers in the region have been retreating since 1850 with increasing melting rates [1]
It clearly shows that both AOD500 and a were consistently higher during January to May, remained low during June to September and started increasing from October till December
The positive a9 indicates the dominance of fine mode aerosol during dry season whereas negative a9 indicates the dominance of coarse mode aerosol during wet season
Summary
The increase in the loading of atmospheric aerosols (locally generated and long-range transported) over the Himalaya is a matter of concern, since most of the glaciers in the region have been retreating since 1850 with increasing melting rates [1]. The loading of atmospheric particulate matter (aerosol) in the eastern Himalaya is mainly regulated by the locally generated anthropogenic aerosols from the biomass burning and by the aerosols transported from the distance sources. These different types of aerosol loading affect the aerosol chemistry and produce consequent signature on the radiative properties of aerosol
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