Different atmospheric O3 chemical environment in industrial regions of China, 2016: implications for emission control strategies and impacts on the globe in the future

Surface ozone (O₃) pollution became the main cause of atmospheric pollution over industrial regions in China since 2013, due to the effective mitigation of fine particulate matter (PM_2.5) by stringent emission controls by Air Pollution Prevention and Control Action Plan (APPCAP). O₃, as a secondary photochemical pollutant, poses a challenge to control due to its non-linear chemical relationship to precursors – nitrogen oxides (NO_x), carbon monoxide (CO) and volatile organic compounds (VOCs).

We hence investigated the differences of atmospheric chemistry environment in the main industrial regions with high emissions – North China Plain (NCP), Yangtze River Delta (YRD), Pearl River Delta (PRD) and Chongqing - in summer 2016, China by using a global climate-chemistry model, based on United Kingdom Chemistry and Aerosol (UKCA). Anthropogenic Multi-resolution Emission Inventory for China (MEIC) 2013 and Hemispheric Transport of Air Pollution (HTAP) emissions 2010 for the rest of globe were used but scaled to 2016 regionally and nationally separately. In addition, we improved the gas-phase chemistry scheme by adding more highly reactive VOC tracers to better simulate regional pollution. Diurnal cycles of O₃ and NO_x have been evaluated and the results show very good model-observation comparisons after modifying the gas-phase chemistry scheme. Radical (OH, RO₂ and HO₂), NO_x and VOC concentrations have also been examined. O₃ production rates and budgets calculated based on these show the highest production rate in YRD and the lowest in PRD due to different NO_x and VOC concentration levels.

To investigate the O₃ sensitivity — VOC limited or NO_x limited, we quantified the O₃ response to VOCs and NO_x in total 64 scenarios by scaling NO_x and VOCs emissions. O₃ isopleths suggest that most regions are VOC limited, but the sensitivities vary. O₃ in YRD is more sensitive to NO_x emission change but PRD can be effectively controlled by decreasing VOC emissions. The ratio of H₂O₂ to HNO₃ is applied to provide a quick examination method of O₃ sensitivity. The contribution of O₃ from China to the global O₃ burden compared with other continents has also been quantified. The results show that the relatively higher O₃ concentration in Asia is mainly contributed by China, and O₃ becomes more sensitive to VOCs. The model allows us to provide a quantitative assessment of different emission controls on mitigating O₃ over China and the impacts of Chinese emissions on the global O₃ burden.