A082-03
Evaluating the sensitivity of radical chemistry and ozone formation to ambient VOCs and NOx in Beijing
Thursday, 10 December 2020: 04:08
Virtual
Lisa Whalley1, Eloise Slater2,3, Robert Woodward-Massey3, Chunxiang Ye4, James D Lee5, Freya Anne Squires5, James R Hopkins5, Rachel Dunmore5, Marvin Shaw6, Jacqueline Hamilton5, Alastair C Lewis6, Archit Mehra7, Stephen D Worrall8, Asan Bacak9, Tom Bannan7, Hugh Coe10, Bin Ouyang11, Roderic L Jones11, Leigh Crilley12, Louisa J Kramer12,13, William Bloss12, Tuan Vu14, Simone Kotthaus15, Sue B Grimmond16, Yele Sun17, Siyao Yue17, Lujie Ren18, W. Joe F. Acton19, C Nick Hewitt19, Xinming Wang20, Pingqing Fu21 and Dwayne E Heard1, (1)University of Leeds, School of Chemistry, Leeds, LS2, United Kingdom, (2)University of Leeds, School of Chemsitry, Leeds, AL, United Kingdom, (3)University of Leeds, School of Chemistry, Leeds, United Kingdom, (4)Peking University, Beijing, China, (5)University of York, Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, York, United Kingdom, (6)Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York, United Kingdom, (7)University of Manchester, Manchester, United Kingdom, (8)Aston University, Chemical Engineering and Applied Chemistry, Birmingham, United Kingdom, (9)University of Manchester, Centre for Atmospheric Science, School of Earth, Atmospheric and Environmental Sciences, Manchester, United Kingdom, (10)Department of Earth and Environmental Sciences, University of Manchester, Manchester, United Kingdom, (11)University of Cambridge, Cambridge, United Kingdom, (12)University of Birmingham, School of Geography, Earth and Environmental Sciences, Birmingham, United Kingdom, (13)University of Birmingham, Birmingham, MI, United Kingdom, (14)University of Birmingham, Birmingham, United Kingdom, (15)King's College London, Department of Geography, London, United Kingdom, (16)University of Reading, Meteorology, Reading, RG6, United Kingdom, (17)Institute of Atmospheric Physics, Chinese Academy of Sciences, State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Beijing, China, (18)Institute of Surface-Earth System Science, Tianjin University, Tianjin, China, (19)University of Lancaster, Lancaster Environment Centre, Lancaster, United Kingdom, (20)Chinese Academy Of Sciences, Guangzhou, China, (21)Tianjin University, Institute of Surface-Earth System Science, Tianjin, China
Abstract:
Despite substantial reductions in primary emissions of pollutants in China over the past decade, concentrations of the secondary pollutant, ozone, still frequently exceed air quality threshold limits in urban areas during the summertime. Understanding the sources and sinks of OH in the atmosphere and the chemical cycling between peroxy radicals is essential to understand ozone formation.
We will present measurements of OH, HO2, RO2-complex (alkene and aromatic-related RO2) and total RO2 radicals taken during in central Beijing in the summer of 2017, alongside observations of OH reactivity. The concentrations of radicals were elevated with OH reaching up to 2.8 x 107 molecule cm-3, HO2 peaked at 1 x 109 molecule cm-3 and the total RO2 concentration reached 5.5 x 109 molecule cm-3. OH reactivity peaked at 89 s-1 during the night, with a minimum during the afternoons of ~22 s-1 on average.
Model comparisons of the radicals have displayed varying levels of agreement as a function of NOx. Under low NO conditions, we will show that there is a missing OH source. Radical budget analysis has demonstrated that this missing OH source could be resolved if unimolecular reactions of RO2 radicals generate OH directly. The model under-predicted RO2, most severely under high NO conditions (>1 ppbv). Although Cl atoms could increase the concentration of RO2, this enhancement was limited to times when the Cl atom concentration was elevated and could not resolve the RO2 under-prediction observed at all times. In the presence of NO, the model over-estimates the rate at which RO2 propagates to HO2 and we hypothesise that larger RO2 species likely undergo multiple bimolecular reactions with NO, followed by isomerisation of the RO radical to another RO2 species, before a HO2 radical forms. By this process, the lifetime and the concentration of total-RO2 radicals is extended. The ozone production efficiency of large, complex VOCs from which these RO2 species are formed may be greater than currently appreciated, and so further efforts to understand the rate at which the larger RO2 species propagate to HO2 (or to OH directly) and all the possible reactions they undergo, is necessary to accurately model ozone levels in urban centres such as Beijing and to fully understand how emission controls will impact ozone.
