Title | Evaluating the sensitivity of radical chemistry and ozone formation to ambient VOCs and NOx in Beijing |
Authors | Whalley, Lisa K. Slater, Eloise J. Woodward-Massey, Robert Ye, Chunxiang Lee, James D. Squires, Freya Hopkins, James R. Dunmore, Rachel E. Shaw, Marvin Hamilton, Jacqueline F. Lewis, Alastair C. Mehra, Archit Worrall, Stephen D. Bacak, Asan Bannan, Thomas J. Coe, Hugh Percival, Carl J. Ouyang, Bin Jones, Roderic L. Crilley, Leigh R. Kramer, Louisa J. Bloss, William J. Vu, Tuan Kotthaus, Simone Grimmond, Sue Sun, Yele Xu, Weiqi Yue, Siyao Ren, Lujie Acton, W. Joe F. Hewitt, C. Nicholas Wang, Xinming Fu, Pingqing Heard, Dwayne E. |
Affiliation | Univ Leeds, Sch Chem, Leeds LS2 9JT, W Yorkshire, England Univ Leeds, Natl Ctr Atmospher Sci, Leeds LS2 9JT, W Yorkshire, England Univ York, Natl Ctr Atmospher Sci, York YO10 5DD, N Yorkshire, England Univ York, Dept Chem, Wolfson Atmospher Chem Labs, York YO10 5DD, N Yorkshire, England Univ Manchester, Ctr Atmospher Sci, Sch Earth & Environm Sci, Manchester M13 9PL, Lancs, England Univ Manchester, Natl Ctr Atmospher Sci, Manchester M13 9PL, Lancs, England CALTECH, Jet Prop Lab, Pasadena, CA USA Univ Cambridge, Dept Chem, Cambridge, England Univ Birmingham, Sch Geog Earth & Environm Sci, Birmingham B15 2TT, W Midlands, England Univ Reading, Dept Meteorol, Reading, Berks, England Ecole Polytech, Inst Pierre Simon Lapl, Palaiseau, France Chinese Acad Sci, Inst Atmospher Phys, State Key Lab Atmospher Boundary Layer Phys & Atm, 40 Huayanli, Beijing 100029, Peoples R China Univ Lancaster, Lancaster Environm Ctr, Lancaster LA1 4YW, England Chinese Acad Sci, Guangzhou Inst Geochem, State Key Lab Organ Geochem, 511 Kehua St, Guangzhou 510640, Peoples R China Tianjin Univ, Inst Surface Earth Syst Sci, Tianjin 300072, Peoples R China Peking Univ, Coll Environm Sci & Engn, Beijing 100871, Peoples R China Univ Chester, Fac Sci & Engn, Chester CH2 4NU, Cheshire, England Aston Univ, Sch Engn & Appl Sci, Aston Inst Mat Res, Birmingham B4 7ET, W Midlands, England Ankara Univ, Turkish Accelerator & Radiat Lab, Atmospher & Environm Chem Lab, Inst Accelerator Technol, Golbasi Campus, Ankara, Turkey York Univ, Dept Chem, Toronto, ON M3J 1P3, Canada |
Issue Date | 12-Feb-2021 |
Publisher | ATMOSPHERIC CHEMISTRY AND PHYSICS |
Abstract | Measurements of OH, HO2, complex RO2 (alkene- and aromatic-related RO2) and total RO2 radicals taken during the integrated Study of AIR Pollution PRO-cesses in Beijing (AIRPRO) campaign in central Beijing in the summer of 2017, alongside observations of OH reactivity, are presented. The concentrations of radicals were elevated, with OH reaching up to 2.8 x 10(7) molecule cm(-3), HO2 peaking at 1 x 10(9) molecule cm(-3) and the total RO2 concentration reaching 5.5 x 10(9) molecule cm(-3). OH reactivity (k(OH)) peaked at 89 s(-1) during the night, with a minimum during the afternoon of approximate to 22 s(-1) on average. An experimental budget analysis, in which the rates of production and destruction of the radicals are compared, highlighted that although the sources and sinks of OH were balanced under high NO concentrations, the OH sinks exceeded the known sources (by 15 ppbv h(-1)) under the very low NO conditions (< 0.5 ppbv) experienced in the afternoons, demonstrating a missing OH source consistent with previous studies under high volatile organic compound (VOC) emissions and low NO loadings. Under the highest NO mixing ratios (104 ppbv), the HO2 production rate exceeded the rate of destruction by approximate to 50 ppbv h(-1), whilst the rate of destruction of total RO2 exceeded the production by the same rate, indicating that the net propagation rate of RO2 to HO2 may be substantially slower than assumed. If just 10 % of the RO2 radicals propagate to HO2 upon reaction with NO, the HO2 and RO2 budgets could be closed at high NO, but at low NO this lower RO2 to HO2 propagation rate revealed a missing RO2 sink that was similar in magnitude to the missing OH source. A detailed box model that incorporated the latest Master Chemical Mechanism (MCM3.3.1) reproduced the observed OH concentrations well but over-predicted the observed HO2 under low concentrations of NO (< 1 ppbv) and under-predicted RO2 (both the complex RO(2 )fraction and other RO2 types which we classify as simple RO2) most significantly at the highest NO concentrations. The model also under-predicted the observed k (OH) consistently by approximate to 10 s(-1) across all NOx levels, highlighting that the good agreement for OH was fortuitous due to a cancellation of missing OH source and sink terms in its budget. Including heterogeneous loss of HO2 to aerosol surfaces did reduce the modelled HO2 concentrations in line with the observations but only at NO mixing ratios < 0.3 ppbv. The inclusion of Cl atoms, formed from the photolysis of nitryl chloride, enhanced the modelled RO2 concentration on several mornings when the Cl atom concentration was calculated to exceed 1 x 10(4) atoms cm(-3) and could reconcile the modelled and measured RO2 concentrations at these times. However, on other mornings, when the Cl atom concentration was lower, large under-predictions in total RO2 remained. Furthermore, the inclusion of Cl atom chemistry did not enhance the modelled RO2 beyond the first few hours after sunrise and so was unable to resolve the modelled under-prediction in RO2 observed at other times of the day. Model scenarios, in which missing VOC reactivity was included as an additional reaction that converted OH to RO2, highlighted that the modelled OH, HO2 and RO2 concentrations were sensitive to the choice of RO2 product. The level of modelled to measured agreement for HO2 and RO2 (both complex and simple) could be improved if the missing OH reactivity formed a larger RO2 species that was able to undergo reaction with NO, followed by isomerisation reactions reforming other RO2 species, before eventually generating HO2. In this work an alpha-pinene-derived RO2 species was used as an example. In this simulation, consistent with the experimental budget analysis, the model underestimated the observed OH, indicating a missing OH source. The model uncertainty, with regards to the types of RO2 species present and the radicals they form upon reaction with NO (HO2 directly or another RO2 species), leads to over an order of magnitude less O-3 production calculated from the predicted peroxy radicals than calculated from the observed peroxy radicals at the highest NO concentrations. This demonstrates the rate at which the larger RO2 species propagate to HO2, to another RO2 or indeed to OH needs to be understood to accurately simulate the rate of ozone production in environments such as Beijing, where large multifunctional VOCs are likely present. |
URI | http://hdl.handle.net/20.500.11897/605056 |
ISSN | 1680-7316 |
DOI | 10.5194/acp-21-2125-2021 |
Indexed | SCI(E) |
Appears in Collections: | 环境科学与工程学院 |