Low-NO atmospheric oxidation pathways in a polluted megacity

Newland, M.J. and Bryant, D.J. and Dunmore, R.E. and Bannan, T.J. and Joe F. Acton, W. and Langford, B. and Hopkins, J.R. and Squires, F.A. and Dixon, W. and Drysdale, W.S. and Ivatt, P.D. and Evans, M.J. and Edwards, P.M. and Whalley, L.K. and Heard, D.E. and Slater, E.J. and Woodward-Massey, R. and Ye, C. and Mehra, A. and Worrall, S.D. and Bacak, A. and Coe, H. and Percival, C.J. and Nicholas Hewitt, C. and Lee, J.D. and Cui, T. and Surratt, J.D. and Wang, X. and Lewis, A.C. and Rickard, A.R. and Hamilton, J.F. (2021) Low-NO atmospheric oxidation pathways in a polluted megacity. Atmospheric Chemistry and Physics, 21 (3). pp. 1613-1625. ISSN 1680-7316

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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.

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Journal Article
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Atmospheric Chemistry and Physics
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25 Feb 2021 10:48
Last Modified:
20 Sep 2023 01:41