Abstract
Abstract. A long-term, robust observational record of atmospheric black carbon (BC) concentrations at Fukue Island for 2009–2019 was produced by unifying the data from a continuous soot monitoring system (COSMOS) and a Multi-Angle Absorption Photometer (MAAP). This record was then used to analyze emission trends from China. We identified a rapid reduction in BC concentrations of (-5.8±1.5) % yr−1 or −48 % from 2010 to 2018. We concluded that an emission change of (-5.3±0.7) % yr−1, related to changes in China of as much as −4.6 % yr−1, was the main underlying driver. This evaluation was made after correcting for the interannual meteorological variability (IAV) by using the regional atmospheric chemistry model simulations from the Weather Research and Forecasting (WRF) and Community Multiscale Air Quality (CMAQ) models (collectively WRF/CMAQ) with the constant emissions. This resolves the current fundamental disagreements about the sign of the BC emissions trend from China over the past decade as assessed from bottom-up emission inventories. Our analysis supports inventories reflecting the governmental clean air actions after 2010 (e.g., MEIC1.3, ECLIPSE versions 5a and 6b, and the Regional Emission inventory in ASia (REAS) version 3.1) and recommends revisions to those that do not (e.g., Community Emissions Data System – CEDS). Our estimated emission trends were fairly uniform across seasons but diverse among air mass origins. Stronger BC reductions, accompanied by a reduction in carbon monoxide (CO) emissions, occurred in regions of south-central East China, while weaker BC reductions occurred in north-central East China and northeastern China. Prior to 2017, the BC and CO emissions trends were both unexpectedly positive in northeastern China during winter months, which possibly influenced the climate at higher latitudes. The pace of the estimated emissions reduction over China surpasses the Shared Socioeconomic Pathways (SSPs with reference to SSP1, specifically) scenarios for 2015–2030, which suggests highly successful emission control policies. At Fukue Island, the BC fraction of fine particulate matter (PM2.5) also steadily decreased over the last decade. This suggests that reductions in BC emissions started without significant delay when compared to other pollutants such as NOx and SO2, which are among the key precursors of scattering PM2.5.
Highlights
Atmospheric particles containing black carbon (BC) strongly absorb sunlight and reduce the surface albedo of ice and/or snow upon their deposition
At Fukue Island, a rapidly decreasing decadal trend in the atmospheric BC mass concentrations of (−5.8 ± 1.5) % yr−1 was detected in the period between 2009 and 2019
We estimated a −4.6 % yr−1 BC emissions reduction in China over the period 2009–2018. This supports MEIC1.3, ECLIPSE versions 5a and 6b, and REAS version 3.1 inventories that reflect emission reduction policies occurring after 2012, our results suggest an earlier onset of these reductions
Summary
Atmospheric particles containing black carbon (BC) strongly absorb sunlight and reduce the surface albedo of ice and/or snow upon their deposition. Fundamental disagreement remains among bottom-up emission inventories regarding the sign of the emissions trend – especially during 2005 and 2014, which represents the modern reference period for the Coupled Model Intercomparison Project Phase 6 (CMIP6) experiments. This is in sharp contrast to our understanding of the SO2 and NOx emissions trends from China (e.g., Zheng et al, 2018) for which studies have reached fairly consistent conclusions. Reliable long-term mass concentration measurements at regionally representative ground-based sites that are useful for an emissions trend analysis are scarce for BC. In Asia, Zhang et al (2019) reported long-term trends in BC mass concentrations from China’s BC observational NETwork (CBNET). There are issues with the interpretation of the data from aethalometers because of potential artifacts from coexisting scattering particles (Collaud Coen et al, 2010; Virkkula et al, 2007; Saturno et al, 2017)
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