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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 02 Oct 2018

Research article | 02 Oct 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Atmospheric oxidation capacity in Chinese megacities during photochemical polluted season: radical budget and secondary pollutants formation

Zhaofeng Tan1,2, Keding Lu1, Meiqing Jiang1, Rong Su1, Hongli Wang3, Shengrong Lou3, Qingyan Fu4, Chongzhi Zhai5, Qinwen Tan6, Dingli Yue7, Duohong Chen7, Zhanshan Wang8, Shaodong Xie1, Limin Zeng1, and Yuanhang Zhang1,9 Zhaofeng Tan et al.
  • 1State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
  • 2Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Jülich GmbH, Jülich, Germany
  • 3State Environmental Protection Key Laboratory of Formation and Prevention of the Urban Air Complex, Shanghai Academy of Environmental Sciences, Shanghai 200233, China
  • 4Shanghai Environmental Monitoring Center, Shanghai 200235, China
  • 5Ecological and Environmental Monitoring Center of Chongqing, Chongqing 401147, China
  • 6Chengdu Academy of Environmental Sciences, Chengdu 610072, China
  • 7State Environmental Protection Key Laboratory of Regional Air Quality Monitoring, Guangdong Environmental Monitoring Center, Guangzhou 510308, China
  • 8Beijing Key Laboratory of Atmospheric Particulate Monitoring Technology, Beijing Municipal Environmental Monitoring Center, Beijing 100048, China
  • 9Beijing Innovation Center for Engineering Sciences and Advanced Technology, Peking University, 100871, Beijing, China

Abstract. Atmospheric oxidation capacity is the core of converting fresh-emitted substances to secondary pollutants. In this study, we present the in-situ measurements at four Chinese megacities (Beijing, Shanghai, Guangzhou, and Chongqing) in China during photochemical polluted seasons. The atmospheric oxidation capacity is evaluated using an observational-based model with the input of radical chemistry precursor measurements. The radical budget analysis illustrates the importance of HONO and HCHO photolysis, which contribute nearly half of the total radical primary sources. The radical propagation is efficient due to abundant of NO in the urban environments. Hence, the production rate of secondary pollutants, i.e. ozone and fine particle precursors (H2SO4, HNO3, and ELVOCs) is fast resulting in secondary air pollution. The ozone budget demonstrates that strong ozone production occurs in the urban area which results in fast ozone concentration increase locally and further transported to downwind areas. On the other hand, the O3-NOx-VOC sensitivity tests show that ozone production is VOC-limited, among which alkenes and aromatics should be first mitigated for ozone pollution control in the presented four megacities. However, NOx emission control will lead to more server ozone pollution due to the drawback-effect of NOx reduction. For fine particle pollution, the role of HNO3NO3 partitioning system is investigated with a thermal dynamic model (ISORROPIA2) due to the importance of particulate nitrate during photochemical polluted seasons. The strong nitrate acid production converts efficiently to nitrate particles due to high RH and ammonium-rich conditions during photochemical polluted seasons. This study highlights the efficient radical chemistry maintains the atmospheric oxidation capacity in Chinese megacities, which results in secondary pollutions characterized by ozone and fine particles.

Zhaofeng Tan et al.
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Status: final response (author comments only)
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Zhaofeng Tan et al.
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Short summary
We evaluated the atmospheric oxidation capacity (AOC) in four Chinese megacities during photochemical polluted seasons. The chemical production of ozone and particle nitrate were diagnosed through a box model, which can be attributed to daytime radical chemistry. Our work highlights that the formation of both ozone and fine particles is largely driven by the atmospheric radical chemistry in China. Consequently, we suggest the future pollution mitigation strategy shall consider the role of AOC.
We evaluated the atmospheric oxidation capacity (AOC) in four Chinese megacities during...