Rapid reduction of black carbon emissions from China: evidence from 2009–2019 observations on Fukue Island, Japan

Abstract

Abstract. A long-term, robust observational record of atmospheric black carbon (BC) concentrations at Fukue Island for 2009–2019 was produced by unifying data from a continuous soot-monitoring system and a multi-angle absorption photometer. This record was then used to analyze emission trends from China. We identified a rapid reduction in BC concentrations of (−5.8 ± 1.5) % y−1 or −48 % from 2010 to 2018. We concluded that an emission change of (−5.3 ± 0.7) % y−1, related to changes in China of as much as −4.6 % y−1, was the main underlying driver. This evaluation was made after correcting for the interannual meteorological variability, by using regional atmospheric chemistry model simulations (WRF/CMAQ) with constant emissions. This resolves current fundamental disagreements about the sign of the BC emission trend from China over the past decade, assessed from bottom-up emission inventories; our analysis supported inventories reflecting the governmental clean air actions after 2010 (e.g., MEIC1.3, ECLIPSE v5a and v6b, and REAS updated) and recommended revision to those not (e.g., CEDS). Our estimated emission trends were fairly uniform over seasons but diverse among air-mass origins. Stronger BC reductions occurred in regions of South-Central East China, accompanied by CO emission reduction, while weaker BC reductions occurred in North-Central East China and Northeast China. Prior to 2017, the BC and CO emission trends were both unexpectedly positive in Northeast China during winter months, possibly influencing climate at higher latitudes. The pace of emission reduction over China surpasses those of SSP1 scenarios (SSP: shared socioeconomic pathways) for 2015–2030, suggesting highly successful emission control policies. At Fukue Island, the BC fraction of PM2.5 also steadily decreased over the last decade, suggesting that BC emission reduction started without significant delay with respect to other pollutants, such as NOx and SO2, which are among key precursors of scattering PM2.5.

The positive radiative forcing by the substantial SO<sub>2</sub> emission reductions is counteracted by decreased BC concentrations in China over the recent decade

“…1c, d), with the averaged decrease of 25% over East China. The model also captures the inter-annual decline in BC observed at Fukue Island in western Japan, which is attributed to the reduction of the BC emissions in East China (Kanaya et al, 2019). Moreover, annual mean BC burdens decrease by 0.38 mg m −2 for this region and by 0.016 mg m −2 in the northern Pacific (Fig.…”

Investigation of the wet removal rate of black carbon in East Asia: validation of a below- and in-cloud wet removal scheme in FLEXPART v10.4

“…Adopting APT, a useful index for the strength of wet deposition (Kanaya et al, 2016;Kanaya et al, 2019), the magnitude of the BC wet removal rate according to precipitation can be easily characterized by TE. Although some previous studies have investigated wet scavenging schemes in models (Grythe et al, 2017;Croft et al, 2010), those results may include bias due to the effect of inaccurate emission rate because emission rates and deposition terms were not necessarily separated.…”