The mixing state and fractal dimension (D f ) of soot particles are two major factors affecting their absorption capacity and their climate effects. Here we investigated these factors of soot particles found in a typical valley of the southeastern Tibetan Plateau where wood burning in local villages was one major source of soot particles. Our motivation revealed D f and the aging property of soot particles in remote air and discussed their regional climatic implications. We found that 64% of total analyzed particles by number were soot-bearing particles and most of them aged with sulfate or organic coating. The D f sequence is bare-like soot (1.75 ± 0.08) < partly coated soot (1.82 ± 0.05) < embedded soot (1.88 ± 0.05). The aging process enlarged the overall size of the soot-bearing particles and increased the compactness of soot. Soot aging critically depended on high relative humidity (RH) during nighttime. Besides emission sources and coating processes, the coating aerosol phase under different RHs is another important factor affecting the soot D f .
Black carbon (BC), emitted by incomplete combustion of biomass and fossil fuels, can strongly absorb sunlight in the atmosphere (Bond & Bergstrom, 2006). BC can transform electromagnetic energy into thermal energy and heat the atmosphere (Buseck et al., 2014) and is one of the most important aerosol components affecting radiative forcing in the atmosphere (Jacobson, 2001). Moreover, BC can indirectly affect the climate through influencing the albedo and lifetime of clouds, snow, and ice (Flanner et al., 2007;Koch & Del Genio, 2010;Menon et al., 2010). Understanding the optical properties of BC is necessary to estimate its
Global models estimate the effects of BC absorption based on its mass concentration, size distribution, particle morphology, and mixing structures of BC particles (Ramanathan & Carmichael, 2008;Riemer et al., 2019). Experimental evidence showed that the absorption enhancement, induced by mixing of BC with other nonabsorbing secondary aerosols, can be less than 1.05 (Cappa et al., 2012;Healy et al., 2015) or as large as 2. 4 (Peng et al., 2016). Furthermore, absorption enhancement obtained using the core-shell Mie theory based on BC coating thickness measured by single particle soot photometer (SP2) or soot particle-aerosol mass spectrometer (SP-AMS) is ∼14%-150% larger than the directly measured ones in field campaigns (
Because of the rapid development of urbanization and industrialization and rise of economy, China has frequently experienced haze pollution. These haze pollution events profoundly affect human health, such as
Soot, also known as black carbon (BC), is a typical aerosol particle. It plays the major role of light-absorbing carbonaceous component of fine particles and forms during the incomplete combustion of biomass and fossil fuels (Bond et al., 2013). Soot particle has been considered as the second largest anthropogenic radiative forcer in the present-day climate after CO 2 (Boucher et al., 2013). It plays a significant role in global warming by affecting the radiative balance at both global and regional scales (
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