A Numerical Study Of Impacts Of Biomass Burning And Transport On Interannual Variation Of Atmospheric Black Carbon Over The Tibetan Surface

As an important component of atmospheric aerosols,black carbon(BC)plays an important role in regional and global climate change.BC over the Tibetan plateau can cause glaciers melting and atmospheric circulation changing,which will change the global climate.Due to the lack of observations,our understanding of the spatial distribution and temporal variation of BC in the Tibetan Plateau is rather limited.In this study,using a three-dimensional global chemical transport model GEOS-Chem,we analyze the spatial distribution characteristics of surface BC aerosols over the Tibetan Plateau and the seasonal variation from 1995 to 2004.Surface BC concentrations over the Tibetan Plateau decrease from the edges to the center.The average concentrations of surface BC over the entire plateau are the highest in winter and the lowest in summer,while surface BC concentrations on the central plateau peak in spring instead of winter.The reason for the difference in the season when surface BC peaks between the entire plateau and central plateau can be explained by the different convergence of air flow over the plateau in spring and winter.The HYSPLT backward trajectories and the results from GEOS-Chem model are combined to calculate the absolute amount and relative value of surface BC contribution from different source regions.The results show that South Asia and EastAsia are the two dominant source regions,and contributions from South Asia decrease from winter to spring while contributions from East Asia increase.From 1995 to 2004,biomass burning emissions and transport from source regions can well explain the interannual variation of surface BC concentrations on the Tibetan plateau.In spring,biomass burning emissions,especially the biomass burning emission in the vegetation covered areas located at the southern edge of the plateau,have a greater influence on the interannual variation of surface BC concentrations than transport.In winter,transport from outside has a greater impact on the interannual variation of surface BC concentrations than biomass burning.Using the Indian monsoon index(IMI),it is found that there is a close relationship between the South Asian monsoon and surface BC concentrations on the Tibetan Plateau.In spring,most areas on the plateau show the positive correlation.The stronger the South Asian monsoon,the stronger the transport of surface BC from South Asia,and the higher the surface BC concentrations on the Tibetan Plateau.In contrast,in winter,the stronger the South Asian winter monsoon,the more unfavorable it is for transport of surface BC from South Asia,and the lower the surface BC concentrations in the Tibetan Plateau.These findings may help understand the temporal variation and spatial distribution of snow melting caused by surface BC over the Tibetan Plateau.