Abstract
Abstract. The source attributions for mass concentration, haze formation, transport and direct radiative forcing of black carbon (BC) in various regions of China are quantified in this study using the Community Earth System Model (CESM) with a source-tagging technique. Anthropogenic emissions are from the Community Emissions Data System that is newly developed for the Coupled Model Intercomparison Project Phase 6 (CMIP6). Over north China where the air quality is often poor, about 90 % of near-surface BC concentration is contributed by local emissions. Overall, 35 % of BC concentration over south China in winter can be attributed to emissions from north China, and 19 % comes from sources outside China in spring. For other regions in China, BC is largely contributed from nonlocal sources. We further investigated potential factors that contribute to the poor air quality in China. During polluted days, a net inflow of BC transported from nonlocal source regions associated with anomalous winds plays an important role in increasing local BC concentrations. BC-containing particles emitted from East Asia can also be transported across the Pacific. Our model results show that emissions from inside and outside China are equally important for the BC outflow from East Asia, while emissions from China account for 8 % of BC concentration and 29 % in column burden in the western United States in spring. Radiative forcing estimates show that 65 % of the annual mean BC direct radiative forcing (2.2 W m−2) in China results from local emissions, and the remaining 35 % is contributed by emissions outside of China. Efficiency analysis shows that a reduction in BC emissions over eastern China could have a greater benefit for the regional air quality in China, especially in the winter haze season.
Highlights
Black carbon (BC), as a component of atmospheric fine particulate matter (PM2.5), is harmful to human health (Anenberg et al, 2011; Janssen et al, 2012)
The BC emissions used in the simulation include a seasonal variability that could cause some variations in simulated concentrations, the monthly variability in DJF of BC emissions is less than 4 % over China, which is negligible compared to the differences in concentrations between polluted and normal days
Unlike the direct radiative forcing (DRF) efficiencies, the near-surface concentration efficiencies over eastern China are similar and even larger than those for central and western China. These results suggest that a reduction in BC emissions in eastern China could have a greater benefit for the regional air quality in China, especially in the winter haze season
Summary
Black carbon (BC), as a component of atmospheric fine particulate matter (PM2.5), is harmful to human health (Anenberg et al, 2011; Janssen et al, 2012). In addition to its impact on air quality, as the most efficient light-absorbing anthropogenic aerosols, BC is thought to exert a substantial influence on climate (Bond et al, 2013; IPCC, 2013; Liao et al, 2015). It can heat the atmosphere through absorbing solar radiation (Ramanathan and Carmichael, 2008), influence cloud microphysical and dynamical processes (Jacobson, 2006; McFarquhar and Wang, 2006), and reduce surface albedo through deposition on snow and ice (Flanner et al, 2007; Qian et al, 2015). Using the Regional Climate Chemistry Modeling System (RegCCMs), Zhuang et al (2013) reported an annual mean BC DRF of 2–5 W m−2 at TOA over eastern China and about 6 W m−2 over the Sichuan Basin in 2006. Li et al (2016) showed a strong DRF of BC over the North China Plain and the Sichuan Basin in most seasons except for spring when the strongest BC DRF with values of 4– 6 W m−2 shifted to southern China
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