Abstract. Atmospheric black carbon (BC) in the Tibetan Plateau (TP) can largely impact
regional and global climate. Still, studies on the inter-annual 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 surface BC concentrations over the TP vary
largely in space and by season, reflecting complicated interplays of BC
sources from different origins. Of all areas in the TP, surface BC
concentrations are highest over the eastern and southern TP, where surface
BC is susceptible to BC transport from East Asia and South Asia,
respectively. Applying a backward-trajectory method that combines BC
concentrations from GEOS-Chem and trajectories from the Hybrid
Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, we assess
the contributions of worldwide source regions to surface BC in the TP. We
estimate that on the 20-year average, 77 % of surface BC in the TP comes from
South Asia (43 %) and East Asia (35 %). Regarding seasonal variation in
non-local influences, South Asia and East Asia are dominant source regions in
winter and summer, respectively, in terms of the amount of BC imported.
However, in terms of affected areas in the TP, South Asia is the dominant
contributor throughout the year. Inter-annually, surface BC over the TP is
largely modulated by atmospheric transport of BC from non-local 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 inter-annual variation in the amount of BC
transported to the TP from non-local regions. In summer, a stronger East
Asian summer monsoon and a stronger South Asian summer monsoon tend to, respectively,
lead to more BC transport from central China and north-eastern South Asia to
the TP. In winter, BC transport from central China is enhanced in years with
a strong East Asian winter monsoon or a strong Siberian High. A stronger Siberian
High can also bring more BC from northern South Asia to the TP. This study
underscores the impacts of atmospheric transport and biomass burning on the
inter-annual variation in surface BC over the TP. It reveals a close
connection between the Asian monsoon and atmospheric transport of BC from
non-local regions to the TP.
Impacts of atmospheric transport and biomass burning on the inter-annual variation in black carbon aerosols over the Tibetan Plateau
