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Discussion papers
https://doi.org/10.5194/acp-2019-29
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-29
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 28 Jan 2019

Research article | 28 Jan 2019

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

Photochemical impacts of haze pollution in an urban environment

Michael Hollaway1, Oliver Wild1, Ting Yang2, Yele Sun2,3, Weiqi Xu2,3, Conghui Xie2,3, Lisa Whalley4,5, Eloise Slater4, Dwayne Heard4,5, and Dantong Liu6,7 Michael Hollaway et al.
  • 1Lancaster Environment Centre, Lancaster University, Bailrigg, Lancaster, UK
  • 2State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
  • 3University of Chinese Academy of Sciences, Beijing 100049, China
  • 4School of Chemistry, University of Leeds, Leeds, UK
  • 5National Centre for Atmospheric Science, University of Leeds, Leeds UK
  • 6Department of Atmospheric Sciences, School of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang, China
  • 7Centre for Atmospheric Sciences, School of Earth and Environmental Sciences, University of Manchester, Manchester, UK

Abstract. Rapid economic growth in China over the past 30 years has resulted in significant increases in the concentrations of small particulates (PM2.5) over the city of Beijing. In addition to health problems, high aerosol loading can impact visibility and thus reduce photolysis rates over the city leading to potential implications for photochemistry. Photolysis rates are highly sensitive not only to the vertical distribution of aerosols but also to their composition as this can impact how the incoming solar radiation is scattered or absorbed. This study, for the first time, uses aerosol composition measurements and lidar optical depth to drive the Fast-JX photolysis scheme and quantify the photochemical impacts of different aerosol species during the Air Pollution and Human Health (APHH) measurement campaigns in Beijing in November–December 2016 and May–June 2017. This work demonstrates that severe haze pollution events (PM2.5 > 75 μg m−3) occur during both winter and summer leading to reductions in O3 photolysis rates of 27.4–34.0 % (greatest in winter) and reductions in NO2 photolysis of 40.4–66.2 % (greatest in summer) at the surface. It also shows that in spite of much lower PM2.5 concentrations in the summer months, the absolute changes in photolysis rates are larger for both O3 and NO2. In the winter, absorbing species such as black carbon dominate the photolysis response to aerosols leading to mean reductions in J[O1D] and J[NO2] in the lowest 1 km of 23.8 % and 23.1 % respectively. In contrast in the summer, scattering aerosol such as organic matter dominate the response leading to mean decreases of 2.0–3.0 % at the surface and increases of 8.4–10.1 % at higher altitudes (3–4 km). During these haze events in both campaigns, the influence of aerosol on photolysis rates dominates over that from clouds. These large impacts on photochemistry can have important implications for concentrations of important atmospheric oxidants such as the hydroxyl radical.

Michael Hollaway et al.
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Michael Hollaway et al.
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This study, for the first time, uses combinations of aerosol and lidar data to drive an offline photolysis scheme. Absorbing species are shown to have the greatest impact on photolysis rate constants in the winter and scattering aerosol are shown to dominate responses in the summer. During haze episodes, aerosols are shown to produce a greater impact than cloud cover. The findings demonstrate the potential photochemical impacts of haze pollution in a highly polluted urban environment.
This study, for the first time, uses combinations of aerosol and lidar data to drive an offline...
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