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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  13 Feb 2020

13 Feb 2020

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This preprint is currently under review for the journal ACP.

Rainforest-like Atmospheric Chemistry in a Polluted Megacity

Mike J. Newland1, Daniel J. Bryant1, Rachel E. Dunmore1, Thomas J. Bannan2, W. Joe F. Acton3, Ben Langford4, James R. Hopkins1,5, Freya A. Squires1, William Dixon1, William S. Drysdale1, Peter D. Ivatt1, Mathew J. Evans1, Peter M. Edwards1, Lisa K. Whalley6,7, Dwayne E. Heard6,7, Eloise J. Slater6, Robert Woodward-Massey8, Chunxiang Ye8, Archit Mehra2, Stephen D. Worrall2,a, Asan Bacak2, Hugh Coe2, Carl J. Percival2,b, C. Nicholas Hewitt3, James D. Lee1,5, Tianqu Cui9, Jason D. Surratt9, Xinming Wang10, Alastair C. Lewis1,5, Andrew R. Rickard1,5, and Jacqueline F. Hamilton1 Mike J. Newland et al.
  • 1Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York, UK
  • 2School of Earth and EnvironmentalSciences, The University of Manchester, Manchester, UK
  • 3Lancaster Environment Centre, Lancaster University, Lancaster, UK
  • 4Centre for Ecology and Hydrology, Edinburgh, EH26 0QB, UK
  • 5National Centre for Atmospheric Science (NCAS), University of York, York, UK
  • 6School of Chemistry, University of Leeds, Leeds, UK
  • 7National Centre for Atmospheric Science, School of Chemistry, University of Leeds, UK
  • 8Beijing Innovation Center for Engineering Science and Advanced Technology, State Key Joint Laboratory for Environmental Simulation and Pollution Control, Center for Environment and Health, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, China
  • 9Department of Environmental Sciences and Engineering, Gillings School of Global Health, University of North Carolina, Chapel Hill, USA
  • 10Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China
  • anow at: Chemical Engineering and Applied Chemistry, School of Engineering and Applied Science, Aston University, Birmingham, UK
  • bnow at: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, USA

Abstract. The impact of volatile organic compound (VOC) emissions to the atmosphere on the production of secondary pollutants, such as ozone and secondary organic aerosol (SOA), is mediated by the concentration of nitric oxide (NO). Polluted urban atmospheres are typically considered to be high-NO environments, while remote regions such as rainforests, with minimal anthropogenic influences, are considered to be low-NO. Policy to reduce urban air pollution is typically developed assuming that the chemistry is controlled by the high-NO regime. However, our observations from central Beijing show that this simplistic separation of regimes is flawed. Despite being in one of the largest megacities in the world, we observe significant formation of gas and aerosol phase oxidation products associated with the low-NO rainforest-like regime during the afternoon. This is caused by a surprisingly low concentration of NO, coupled with high concentrations of VOCs and of the atmospheric oxidant hydroxyl (OH). Box model calculations suggest that during the morning high-NO chemistry predominates (95 %) but in the afternoon low-NO chemistry plays a greater role (30 %). With increasing global emphasis on reducing air pollution, the modelling tools used to develop urban air quality policy need to adequately represent both high- and low-NO regimes if they are to have utility.

Mike J. Newland et al.

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Mike J. Newland et al.

Mike J. Newland et al.


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Short summary
We report the formation of secondary pollutants in the urban Megacity of Beijing that are typically associated with remote regions such as rainforests. This is caused by extremely low levels of nitric oxide (NO), typically expected to be high in urban areas, observed in the afternoon. This work has significant implications for how we understand atmospheric chemistry in the urban environment, and thus how to implement effective policies to improve urban air quality.
We report the formation of secondary pollutants in the urban Megacity of Beijing that are...