Measurement report: Strong light absorption induced by aged biomass burning black carbon over the southeastern Tibetan Plateau in pre-monsoon season
2021
Abstract. During the pre-monsoon season, biomass burning (BB) activities are intensive
in southern Asia. Facilitated by westerly circulation, those BB plumes can
be transported to the Tibetan Plateau (TP). Black carbon (BC), the main
aerosol species in BB emissions, is an important climate warming agent, and
its absorbing property strongly depends on its size distribution and mixing
state. To elucidate the influence of those transported BB plumes on the TP,
a field campaign was conducted on the southeast edge of the TP during the
pre-monsoon season. It was found that the transported BB plumes
substantially increased the number concentration of the atmospheric BC
particles by a factor of 13 and greatly elevated the number fraction of
thickly coated BC from 52 % up to 91 %. Those transported BC particles
had slightly larger core size and much thicker coatings than the background
BC particles. However, the coating mass was not evenly distributed on BC
particles with different sizes. The smaller BC cores were found to have
larger shell / core ratios than the larger cores. Besides, the transported BB
plumes strongly affected the vertical variation in the BC's abundance and
mixing state, resulting in a higher concentration, larger number fraction,
and higher aging degree of BC particles in the upper atmosphere. Resulting
from both increase in BC loading and aging degree, the transported BB plumes
eventually enhanced the total light absorption by a factor of 15, of which 21 %
was contributed by the BC aging, and 79 % was contributed from the
increase in BC mass. Particularly, the light absorption enhancement induced
by the aging process during long-range transport has far exceeded the
background aerosol light absorption, which implicates a significant
influence of BC aging on climate warming over the TP region.
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