Preprints
https://doi.org/10.5194/acp-2022-207
https://doi.org/10.5194/acp-2022-207
11 Apr 2022
 | 11 Apr 2022
Status: this preprint has been withdrawn by the authors.

Radical chemistry at a UK coastal receptor site – Part 1: observations of OH, HO2, RO2, and OH reactivity and comparison to MCM model predictions

Robert Woodward-Massey, Roberto Sommariva, Lisa K. Whalley, Danny R. Cryer, Trevor Ingham, William J1 Bloss, Sam Cox, 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. OH, HO2, total and partially-speciated RO2, and OH reactivity (kOH) were measured during the July 2015 ICOZA (Integrated Chemistry of OZone in the Atmosphere) project that took place at a coastal site in North Norfolk, UK. Maximum measured daily OH, HO2, and total RO2 radical concentrations were in the range 2.6–17 × 106, 0.75–4.2 × 108, and 2.3–8.0 × 108 molecule cm−3, respectively. k'OH ranged from 1.7 to 17.6 s−1 with a median value of 4.7 s−1. ICOZA data were split by wind direction to assess differences in the radical chemistry between air that had passed over the North Sea (NW–SE sectors) or major urban conurbations such as London (SW sector). A photostationary steady-state (PSS) calculation underpredicted daytime OH in NW–SE air by ~35 %, whereas agreement (~15 %) was found within instrumental uncertainty (~26 % at 2σ) in SW air. A box model using MCMv3.3.1 chemistry was in better agreement with the OH measurements, but it overpredicted HO2 observations in NW–SE air in the afternoon by a factor of ~2–3, although slightly better agreement was found for HO2 in SW air (factor of ~1.4–2.0 underprediction). The box model severely underpredicted total RO2 observations in both NW–SE and SW air by factors of ~8–9 on average. Measured radical and kOH levels and measurement-to-model ratios displayed strong dependences on NO mixing ratios. The PSS calculation could capture OH observations at high NO but underpredicted the observations at low NO. The box model overpredicted HO2 concentrations at low NO in NW–SE air, whereas in SW air, the measurements and model results were in agreement across the full NO range. The box model underpredicted total RO2 at all NO levels, where the measurement-to-model ratio scaled with NO. This trend has been found in all previous field campaigns in which total RO2 was measured using the ROxLIF technique and suggests that peroxy radical chemistry is not well understood under high NOx conditions.

This preprint has been withdrawn.

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Robert Woodward-Massey, Roberto Sommariva, Lisa K. Whalley, Danny R. Cryer, Trevor Ingham, William J1 Bloss, Sam Cox, 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

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-207', Anonymous Referee #1, 01 May 2022
    • AC1: 'Response to Reviewer 1', Dwayne Heard, 16 Jan 2023
  • RC2: 'Comment on acp-2022-207', Anonymous Referee #2, 22 May 2022
    • AC2: 'Reply on RC2', Dwayne Heard, 16 Jan 2023

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-207', Anonymous Referee #1, 01 May 2022
    • AC1: 'Response to Reviewer 1', Dwayne Heard, 16 Jan 2023
  • RC2: 'Comment on acp-2022-207', Anonymous Referee #2, 22 May 2022
    • AC2: 'Reply on RC2', Dwayne Heard, 16 Jan 2023
Robert Woodward-Massey, Roberto Sommariva, Lisa K. Whalley, Danny R. Cryer, Trevor Ingham, William J1 Bloss, Sam Cox, 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
Robert Woodward-Massey, Roberto Sommariva, Lisa K. Whalley, Danny R. Cryer, Trevor Ingham, William J1 Bloss, Sam Cox, 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

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Short summary
We measured radicals (OH, HO2, RO2) and OH reactivity at a UK coastal site and compared our observations to the predictions of an MCMv3.3.1 box model. We find variable agreement between measured and modelled radical concentrations and OH reactivity, where the levels of agreement for individual species display strong dependences on NO concentrations. The most substantial disagreement is found for RO2 at high NO (> 1 ppbv), when RO2 levels are underpredicted by a factor of ~10–30.
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