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

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-Massey1, Roberto Sommariva2,4, Lisa K. Whalley1,3, Danny R. Cryer1, Trevor Ingham1, William J1 Bloss4, Sam Cox5,a, James D. Lee6,7, Chris P. Reed6,b, Leigh R. Crilley4,c, Louisa J. Kramer4,d, Brian J. Bandy8, Grant L. Forster9, Claire E. Reeves8, 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
  • 5Research Software Engineering Team, University of Leicester, Leicester, LE1 7RH, UK
  • 6Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York, YO10 5DD, UK
  • 7National Centre for Atmospheric Science, University of York, York, YO10 5DD, UK
  • 8Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia, Norwich, UK
  • 9National Centre for Atmospheric Science, University of East Anglia, Norwich, NR4 7TJ, UK
  • anow at: Digital Research Service, University of Nottingham, Nottingham, NG7 2RD, UK
  • bnow at: Faculty for Airborne Atmospheric Measurements, Cranfield University, Cranfield, MK43 0AL, UK
  • cnow at: Department of Chemistry, York University, Toronto, M3J 1P3, Canada
  • dnow at: Ricardo Energy & Environment, Harwell, Oxfordshire, OX11 0QR, UK

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.

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-2022-207', 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 et al.

Robert Woodward-Massey et al.


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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.