Changes in inorganic aerosol compositions over the Yellow Sea area from impact of Chinese emissions mitigation.

Substantial mitigation of air pollutants emissions has been performed since 2013 around Beijing, and changes in the atmospheric characteristics have been expected over the downstream area of Beijing. In this study, both WRF-Chem simulation and on-site measurements were utilized for the Baengnyeong (island) supersite, one of the representative regional background sites located in the Yellow Sea, the entrance area of the long-range transport process in Korea. The changes in the chemical compositions of inorganic aerosols were examined for spring-time during the Chinese emission mitigation period from 2014 to 2016. The measured ratio of ionic species to PM 2.5 at the Baengnyeong supersite showed changes in aerosol inorganic chemical compositions from sulfate in 2014 to nitrate in 2015–2016. The modeling results also showed that nitrate was low in 2014 and significantly increased in 2015 and 2016, and the acidic aerosol condition had also changed toward a more neutralized status in both the simulation and the observations. The WRF-Chem modeling study further indicated that the sulfur was not neutralized in 2014. However, in 2015 and 2016, SO 2 was more sufficiently neutralized as sulfur emissions were substantially reduced in China, while at the same time nitrate had begun to increase in such a 'SO 2 –poor' condition in Beijing area in China, and thus approaching more enhanced neutralization over the Yellow Sea area. The causes of the higher nitrate based on the modeled characteristics of the ammonia-sulfate-nitrate aerosol formation in response to the SO 2 emissions reduction in China are also discussed in this paper. Inorganic composition is changing from sulfate to nitrate, and aerosol acidity is approaching more enhanced neutralization over regional background area in Northeast Asia. Unlabelled Image • Inorganic components were examined over background area during Beijing's emission reduction. • Observations showed significant change in decreased sulfate and opposite trend in nitrate. • Aerosol acidity changed to enhanced nitrate neutralization through the emission reduction period. • More enhanced nitrate was also simulated by WRF-Chem mainly due to Beijing's emission mitigation. [ABSTRACT FROM AUTHOR]