04 Apr 2022
04 Apr 2022
Status: this preprint is currently under review for the journal ACP.

Radical chemistry at a UK coastal receptor site – Part 2: experimental radical budgets and ozone production

Robert Woodward-Massey1, Roberto Sommariva2,4, Lisa K. Whalley1,3, Danny R. Cryer1, Trevor Ingham1, William J. Bloss4, Stephen M. Ball2, James D. Lee5,6, Chris P. Reed5,a, Leigh R. Crilley4,b, Louisa J. Kramer4,c, Brian J. Bandy7, Grant L. Forster8, Claire E. Reeves7, Paul S. Monks2, and Dwayne E. Heard1 Robert Woodward-Massey et al.
  • 1School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK
  • 2School of Chemistry, University of Leicester, University Road, Leicester, LE1 7RH, UK
  • 3National Centre for Atmospheric Science, University of Leeds, Leeds, LS2 9JT, UK
  • 4School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UK
  • 5Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York, YO10 5DD, UK
  • 6National Centre for Atmospheric Science, University of York, York, YO10 5DD, UK
  • 7Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia, Norwich, UK
  • 8National Centre for Atmospheric Science, University of East Anglia, Norwich, NR4 7TJ, UK
  • anow at: Faculty for Airborne Atmospheric Measurements, Cranfield University, Cranfield, MK43 0AL, UK
  • bnow at: Department of Chemistry, York University, Toronto, M3J 1P3, Canada
  • cnow at: Ricardo Energy & Environment, Harwell, Oxfordshire, OX11 0QR, UK

Abstract. In our companion paper (Woodward-Massey et al., 2022), we presented measurements of radical species and OH reactivity (k OH) made in summer 2015 during the ICOZA (Integrated Chemistry of OZone in the Atmosphere) field campaign at the Weybourne Atmospheric Observatory, a site on the east coast of the UK. In the present work, we used the simultaneous measurement of OH, HO2, total RO2, and k OH to derive experimental (i.e., observationally determined) budgets for all radical species as well as total ROx (= OH + HO2 + RO2). Data were separated according to wind direction: prevailing SW winds (with influence from London and other major conurbations), and all other winds (NW–SE; predominantly marine in origin). In NW–SE air, the ROx budget could be closed during the daytime within experimental uncertainty but OH destruction exceeded OH production, and HO2 production greatly exceeded HO2 destruction while the opposite was true for RO2. In SW air, the ROx budget analysis indicated missing daytime ROx sources but the OH budget was balanced, and the same imbalances were found with the HO2 and RO2 budgets as in NW–SE air. For HO2 and RO2, the budget imbalances were most severe at high NO mixing ratios.

We explored several mechanistic modifications to the experimental budgets to try to reconcile the HO2 and RO2 budget imbalances: (1) the addition of generic radical recycling processes, (2) reduction of the rate of RO2 → HO2 conversion, (3) inclusion of heterogeneous HO2 uptake, and (4) addition of chlorine chemistry. The best agreement between HO2 and RO2 production and destruction rates was found for option (2), in which we reduced the RO2 + NO rate constant by a factor of 5.

The rate of in situ ozone production (P(Ox)) was calculated from observations of ROx, NO, and NO2 and compared to that calculated from MCM-modelled radical concentrations. The MCM-calculated P(Ox) significantly underpredicted the measurement-calculated P(Ox) in the morning, and the degree of underprediction was found to scale with NO.

Robert Woodward-Massey et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-213', Anonymous Referee #1, 28 Apr 2022
  • RC2: 'Comment on acp-2022-213', Anonymous Referee #2, 09 May 2022

Robert Woodward-Massey et al.

Robert Woodward-Massey et al.


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Short summary
We performed a radical (OH, HO2, RO2; total ROx) budget analysis on a dataset collected during a field intensive at a UK coastal site. We found significant differences between calculated HO2 and RO2 production and destruction rates, which should be balanced for such highly reactive radicals under steady state conditions. In addition, ozone production rates were calculated from measured radicals and compared to MCMv3.3.1 model predictions.