Potential Effect of Halogens on Atmospheric Oxidation and Air Quality in China. Issue 9 (6th May 2020) - Li, Qinyi
Abstract: Air pollution has been a hazard in China over recent decades threatening the health of half a billion people. Much effort has been devoted to mitigating air pollution in China leading to a significant reduction in primary pollutants emissions from 2013 to 2017, while a continuously worsening trend of surface ozone (O3, a secondary pollutant and greenhouse gas) was observed over the same period. Atmospheric oxidation, dominated by daytime reactions involving hydroxyl radicals (OH), is the critical process to convert freshly‐emitted compounds into secondary pollutants, and is underestimated in current models of China's air pollution. Halogens (chlorine, bromine, and iodine) are known to profoundly influence oxidation chemistry in the marine environment; however, their impact on atmospheric oxidation and air pollution in China is unknown. In the present study, we report for the first time that halogens substantially enhance the total atmospheric oxidation capacity in polluted areas of China, typically 10% to 20% (up to 87% in winter) and mainly by significantly increasing OH level. The enhanced oxidation along the coast is driven by oceanic emissions, and that over the inland areas by anthropogenic emission. The extent and seasonality of halogen impact are largely explained by the dynamics of Asian monsoon, location and intensity of halogen emissions, and O3 formation regime. The omission of halogen emissions and chemistry may lead to significant errors in historical re‐assessments and future projections of the evolution of atmospheric oxidation in polluted regions. Key Points: First assessment of halogen impact on the overall atmospheric oxidation over Chin Halogens result in enhanced oxidation throughout the year in polluted regions in China Large spatio‐temporal heterogeneity of the halogen‐mediated effect on oxidation capacity, which can be explained by the Asian monsoon, the location and intensity of halogen sources, and the ozone formation regime First regional model evaluation of halogen impact on air quality in China