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Sources and Transport of Light-absorbing Aerosols over the Tibetan PlateauCN



Abstract:The Tibetan Plateau(TP),which is known as the“water tower”,embraces the largest magnitude of glacier in the midlatitude region.Because of its high elevation and therefore unique thermal and dynamic effects,it significantly influences the Asian weather and climate.A large number of observations have indicated that the TP has been suffering from foreign pollutants,and some of them such as dust and black carbon(BC)aerosols,showed an upward trend.Due to their strong solar absorption,light-absorbing aerosols can change the atmospheric stability and accelerate snow melting through snow-darkening effect,which is also one of the important factors for TP warming.Therefore,it is of great significance to clarify the source of light-absorbing aerosols over the TP for protecting the ecological security barrier and predicting the future weather and climate change in the TP.In this study,the Weather Research and Forecasting coupled with chemistry(WRF-Chem)model combined with multiple observations was used to investigate the sources and potential transport mechanisms of dust and black carbon aerosols.The major results are shown below:(1)Compared with the observations from surface weather stations,we found that the WRF-Chem model reproduced the spatial-temporal distribution of temperature and precipitation over model domain.The correlation coefficients between modeling temperature and observations exceed 0.96.Model also captured the variability of Aerosol Optical Depth(AOD)in Taklimakan desert(TD),northern India,TP,northern and eastern China,as well as aerosol extinction coefficient.The correlation coefficients between Aerosol Robotic Network AOD and WRF-Chem AOD in SACOL and Kanpur reach 0.6.Regarding near surface BC,the WRF-Chem reasonably simulated its distribution in comparison to samples.However,the WRF-Chem model underestimated the AOD over India and Bangladesh,which may be possibly associated with the uncertainty of anthropogenic emission inventory in South Asia,the difficulty of parameterization schemes in complex terrain and the neglect of year-to-year growth in BC emission.(2)The relationship of dust aerosol between TP and TD and their internal mechanism were investigated.In spite of higher dust emission flux in spring over the TP and TD,the dust mass loading in summer is 90 mg-2 higher than that in spring over the northern TP and Tianshan Mountains.Satellite observations also confirm that higher dust extinction coefficient occurred at 3-8 km over the TD where the dust concentration in summer is 30μg m-3 larger than that in spring.Further analysis of the transport fluxes of TD dust in four directions showed that the meridional output is only inferior to the eastward output of TD dust,especially in summer.From spring to summer,the proportion of eastward transport flux decreased from 74%to 61%significantly,while the southward transport flux increased from 21%to 30%.Although the dust emission is large in spring due to frequent cold fronts,the strong westerly wind brings most of the dust eastward to eastern China,resulting lower dust concentration over the TD.In contrast,dust particles over the TD can be entrained to the altitudes of 3-8 km and suspend in atmosphere due to the weakness of westerly wind and intense sensible heating over desert.At the same time,there is a cyclonic convergence near the surface of northern TP.With the support of topographic lift and northly flow,the TD dust was taken to the TP and penetrate upward,subsequently changing the TP heat source.(3)The source and transport of BC over the TP and its surrounding areas were also investigated.Results show that the east slope of the TP is the most significant area for the daily variation of BC.The weakness of westerly wind over northern TP,acceleration of westerly wind over southern TP,and eastward shift of East Asian major trough are responsible for the high BC concentration over east slope of the TP.Under this circumstance,more BC from northern India can be transported to eastern TP and the south slopes of the TP by the enhanced westerly wind.The intensified southwesterly wind over east slope of the TP brings more BC from the Sichuan Basin to northeastern TP.The BC can also penetrate to eastern TP in planetary boundary layer along with northeasterly wind over central China.Subsequently,the weakened westerly wind over northern TP and positive anomalous updrafts over east slope of the TP support the accumulation and uplift of BC.Another circulation mode is opposite to the pattern mentioned above and results in low BC concentration over the TP.These two circulation modes are possibly associated with the low-level meridional temperature anomaly over East Asia,which modulates the upper-level atmospheric circulation through the transient eddy feedback.
  • Series:

    (B) Chemistry/ Metallurgy/ Environment/ Mine Industry

  • Subject:

    Environment Science and Resources Utilization

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