Impacts of atmospheric transport and biomass burning on the interannual variation in black carbon aerosols over the Tibetan Plateau

Abstract

Abstract. Atmospheric black carbon (BC) in the Tibetan Plateau (TP) can largely impact regional and global climate. Still, studies on the interannual variation in atmospheric BC over the TP and associated variation in BC sources and controlling factors are rather limited. In this study, we characterize the variations in atmospheric BC over the TP surface layer through analysis of 20-year (1995–2014) simulations from a global chemical transport model, GEOS-Chem. The results show that, of all areas in the TP, surface BC concentrations are highest over the eastern and southern TP, where surface BC are susceptible respectively to BC transport from East Asia and South Asia. Combining the GEOS-Chem simulations and trajectories from the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, we assess the contributions of different source regions to surface BC in the TP. On the 20-year average, over 90 % surface BC in the TP comes from South Asia (47 %) and East Asia (46 %). Regarding seasonal variation in foreign influences, South Asia and East Asia are dominant source regions in winter and summer, respectively, in terms of both magnitude and affected areas in the TP. In spring and autumn, the influences from the two source regions are somewhat comparable. Interannually, surface BC over the TP is largely modulated by atmospheric transport of BC from foreign regions year-round and by biomass burning in South Asia, mostly in spring. We find that the extremely strong biomass burning in South Asia in the spring of 1999 greatly enhanced surface BC concentrations in the TP (31 % relative to the climatology). We find that the strength of the Asian monsoon correlates significantly with the interannual variation in the amount of BC transported to the TP from foreign regions. In summer, strong East Asian summer monsoon and South Asian summer monsoon tend to, respectively, increase BC transport from central China and northeast South Asia to the TP. In winter, BC transport from central China is enhanced in years with strong East Asia winter monsoon or Siberian High. A strong Siberian High can also increase BC transport from northern South Asia to the TP. This study underscores the impacts of atmospheric transport and biomass burning on the interannual variation in surface BC over the TP. It reveals a close connection between the atmospheric transport of BC from foreign regions to the TP and the Asian monsoon.

Southern Himalayas rainfall as a key driver of interannual variation of pre-monsoon aerosols over the Tibetan Plateau

“…Observations and modeling show an evident interannual variation in aerosols transported from South Asia to the TP during the pre-monsoon season. Previous studies suggested that biomass burning is an important driver of the interannual variations in aerosols over the TP during pre-monsoon 15 . Relatedly, the interannual variation in meteorological fields could also influence the interannual fluctuations in aerosols over the TP [15][16][17] .…”

“…Previous studies suggested that biomass burning is an important driver of the interannual variations in aerosols over the TP during pre-monsoon 15 . Relatedly, the interannual variation in meteorological fields could also influence the interannual fluctuations in aerosols over the TP [15][16][17] . Focusing on the impacts of winds, large-scale westerlies coupled with valley and glacier winds were found to be essential for aerosol transport toward the TP [18][19][20][21][22][23] .…”

“…Focusing on the impacts of winds, large-scale westerlies coupled with valley and glacier winds were found to be essential for aerosol transport toward the TP [18][19][20][21][22][23] . It is commonly expected that enhanced wind speed would increase aerosol loading over the TP during the pre-monsoon season 15,17 . In particular, Li et al (2020) found a considerable interannual correlation between Arctic sea ice and aerosols over the TP.…”