04 Apr 2022
 | 04 Apr 2022
Status: a revised version of 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-Massey, Roberto Sommariva, Lisa K. Whalley, Danny R. Cryer, Trevor Ingham, William J. Bloss, Stephen M. Ball, James D. Lee, Chris P. Reed, Leigh R. Crilley, Louisa J. Kramer, Brian J. Bandy, Grant L. Forster, Claire E. Reeves, Paul S. Monks, and Dwayne E. Heard

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
    • AC1: 'Response to Referee 1', Dwayne Heard, 16 Jan 2023
  • RC2: 'Comment on acp-2022-213', Anonymous Referee #2, 09 May 2022
    • AC2: 'Response to Referee 2', Dwayne Heard, 16 Jan 2023

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.