Abstract
ABSTRACTSevere PM2.5 air pollution over the Asian continent is occasionally transported across the East China Sea by the westerly winds to Japan, continuing for long distances over the Pacific Ocean. Despite such polluted air masses causing health issues, conventional models tend to underestimate levels of organic aerosols (OA) and PM2.5. Here, PM2.5 and its major components recorded during three field campaigns carried out at Fukue Island (32.75°N, 128.68°E), Japan (spring 2009), Rudong (32.25°N, 121.37°E), China (spring 2010), and Jeju (33.35°N, 126.39°E), Korea (autumn 2012) around the East China Sea were used to test the performance of the Weather Research and Forecasting-Chem/ATRAS-MOSAIC model. Overall, model performance was improved by introducing chemical aging represented by a volatility basis-set scheme, whereby median values of the model/observation ratio for OA were raised to 0.34–1.28 from 0.30–0.35 in the case of conventional settings. In particular, the levels of OA at the Fukue site and daytime buildup of the OA levels at all three sites were reproduced by the model. OA levels were still sometimes underestimated. This suggests that either emission rates of organic precursors are being underestimated or other pathways of OA formation are also important. Our analysis also indicates that this region is characterized by high OH concentrations, promoting chemical aging. The predictions of PM2.5 levels in the model also improved, with median values of the model/observation ratio shifting from 0.67–0.91 to 0.68–0.95, when chemical aging of OA was taken into account.
Highlights
Heavy PM2.5 air pollution in East Asia, which is widespread over several thousands of kilometers, is of concern as an important regional health risk factor
The actual campaign-average mass concentrations of major chemical components and the total PM2.5 mass concentrations are shown in Fig. 2
Mass closure of PM2.5 was almost satisfied with observed quantities at all three sites. These results were used as benchmarks to test the regional-scale WRF-Chem/ATRAS-MOSAIC model simulations representing chemical aging, using the volatility basis-set (VBS) scheme
Summary
Heavy PM2.5 air pollution in East Asia, which is widespread over several thousands of kilometers, is of concern as an important regional health risk factor. Continental outflow from East Asia, dominant in autumn/ winter/spring, carries pollutants for long distances across the East China Sea, while chemical aging on a time scale of days promotes secondary formation of sulfate, nitrate, and Kanaya et al, Aerosol and Air Quality Research, 17: 3091–3105, 2017. A national monitoring network was developed in Japan (Ministry of the Environment of Japan, 2014). This monitoring revealed that above-threshold levels were widely observed over western Japan. Comprehensive observations on the major chemical components of PM2.5 including both organics and inorganics have not been often reported, relevant to such long-range transport; data were only available for specific research missions over western Japan (e.g., Hatakeyama et al, 2011; Takami et al, 2013). In the upstream region of Japan, data at Gosan (33.17°N, 126.09°E) on Jeju Island, Korea (Lim et al, 2012), Baengnyeong Island (37.97°N, 124.63°E) , Korea (Lee et al, 2015), and at Changdao Island (37.93°N and 120.72°E), China, between Bohai Bay and Yellow Sea (Feng et al, 2012) were reported
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