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Low-NO atmospheric oxidation pathways in a polluted megacity

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Author(s)

  • Daniel J. Bryant
  • Thomas J. Bannan
  • W. Joe
  • Ben Langford
  • James R. Hopkins
  • William Dixon
  • Lisa K. Whalley
  • Dwayne E. Heard
  • Eloise J. Slater
  • Robert Woodward-Massey
  • Chunxiang Ye
  • Archit Mehra
  • Stephen D. Worrall
  • Asan Bacak
  • Hugh Coe
  • Carl J. Percival
  • C. Nicholas Hewitt
  • Tianqu Cui
  • Jason D. Surratt
  • Xinming Wang

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Publication details

JournalAtmospheric Chemistry and Physics
DateAccepted/In press - 1 Dec 2020
DatePublished (current) - 8 Feb 2021
Issue number3
Volume21
Number of pages13
Pages (from-to)1613-1625
Original languageEnglish

Abstract

The impact of emissions of volatile organic compounds (VOCs) 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". 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 formation of gas- and aerosol-phase oxidation products usually associated with low-NO "rainforest-like"atmospheric oxidation pathways during the afternoon, caused by extreme suppression of NO concentrations at this time. 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 %). Current emissions inventories are applied in the GEOS-Chem model which shows that such models, when run at the regional scale, fail to accurately predict such an extreme diurnal cycle in the NO concentration. With increasing global emphasis on reducing air pollution, it is crucial for the modelling tools used to develop urban air quality policy to be able to accurately represent such extreme diurnal variations in NO to accurately predict the formation of pollutants such as SOA and ozone.

Bibliographical note

© Author(s) 2021.

Funding Information:
Acknowledgements. We acknowledge the support from Pingqing Fu, Zifa Wang, Jie Li, and Yele Sun from the IAP for hosting the APHH-Beijing campaign at the IAP. We thank Zongbo Shi, Roy Harrison, Tuan Vu, and Bill Bloss from the University of Birmingham; Siyao Yue, Liangfang Wei, Hong Ren, Qiaorong Xie, Wanyu Zhao, Linjie Li, Ping Li, Shengjie Hou, and Qingqing Wang from the IAP; Kebin He and Xiaoting Cheng from Tsinghua University; and James Allan from the University of Manchester for providing logistic and scientific support for the field campaigns. Peter Ivatt acknowledges funding from NCAS through one of its Air Pollution and Human Health studentships. Daniel Bryant, William Dixon, William Drysdale, Freya Squires, and Eloise Slater acknowledge the NERC SPHERES Doctoral Training Partnership (DTP) for studentships.

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