Abstract
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.
Highlights
Biomass burning (BB) is an important source of atmospheric aerosols, exerting a significant impact on the regional and global climate system (von Schneidemesser et al, 2015; Jacobson, 2014)
Aside from the coating thickness, the number fraction of thickly coated Black carbon (BC) is higher in Period I than in Period II, with an average of 81.8 % in Period I compared with an average of 51.7 % in Period II (Fig. 1c)
Every year in the pre-monsoon season, the biomass burning plumes which originated in South and Southeast Asia can be transported to the Tibetan Plateau by the convenience of westerly wind
Summary
Biomass burning (BB) is an important source of atmospheric aerosols, exerting a significant impact on the regional and global climate system (von Schneidemesser et al, 2015; Jacobson, 2014). During the transport in the atmosphere, BC aerosols will experience a complex aging process and gradually become internally mixed with other aerosol species (non-BC coatings), which will lead to a great change in BC’s properties (Jacobson, 2001). Those coatings on BC will enhance the light absorption of BC through the so-called lensing effect (Lack and Cappa, 2010), which will further en-
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