Environmental Sciences Section, Bose Institute, Kolkata, India.
PLoS One. 2012;7(7):e40286. doi: 10.1371/journal.pone.0040286. Epub 2012 Jul 5.
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 not only affect the aerosol chemistry but also produce consequent signature on the radiative properties of aerosol.
METHODOLOGY/PRINCIPAL FINDINGS: An 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 (Ca(2+)) 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 SO(4)(2-) and black carbon) were higher (76% for black carbon and 96% for fine mode SO(4)(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/SIGNIFICANCE: The 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.
喜马拉雅山东部的大气颗粒物（气溶胶）负载主要受生物质燃烧产生的本地人为气溶胶和远距离传输而来的气溶胶调节。这些不同类型的气溶胶负载不仅影响气溶胶化学性质，而且对气溶胶辐射特性产生相应的影响。
方法/主要发现：本研究对喜马拉雅山东部高海拔（2200 米）的大吉岭地区在 2008 年全年的细颗粒和粗颗粒气溶胶以及黑碳的季节变化进行了广泛研究，同时还对晴天的气溶胶光学深度进行了同步测量。我们发现，在季风前（4 月至 5 月）细颗粒粉尘成分（Ca(2+)）的负载量很高，比年平均值高出 162%，而在冬季（12 月至 2 月），主要来自生物质燃烧的人为气溶胶成分（细颗粒 SO(4)(2-)和黑碳）的负载量更高（黑碳高 76%，细颗粒 SO(4)(2-)高 96%）。季风前的粉尘气溶胶和冬季的人为气溶胶的大量增加分别使气溶胶光学深度增加了 25%和 40%。我们发现，在冬季，人为气溶胶每增加 1%，AOD 增加 0.55%；而在季风前，粉尘气溶胶每增加 1%，AOD 增加 0.46%。
结论/意义：自然尘埃传输过程（季风前）对辐射效应的作用与人为生物质燃烧（冬季）一样重要，而且它们的差异效应（AOD 与气溶胶浓度的增长率）也非常相似。在对喜马拉雅山东部大气环境进行适当建模时，应考虑到这一点。
