ACPD

Atmospheric Chemistry and Physics Discussions

ACPD

Atmos. Chem. Phys. Discuss.

1680-7375

Göttingen, Germany

10.5194/acp-2022-207

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

Woodward-Massey

Robert

¹ Sommariva

Roberto

https://orcid.org/0000-0002-2728-5814

² ⁴ Whalley

Lisa K.

¹ ³ Cryer

Danny R.

¹ Ingham

Trevor

¹ Bloss

William J1

https://orcid.org/0000-0002-3017-4461

⁴ Cox

Sam

https://orcid.org/0000-0002-9841-9816

⁵ ¹⁰ Lee

James D.

https://orcid.org/0000-0001-5397-2872

⁶ ⁷ Reed

Chris P.

⁶ ¹¹ Crilley

Leigh R.

https://orcid.org/0000-0003-2268-9956

⁴ ¹² Kramer

Louisa J.

⁴ ¹³ Bandy

Brian J.

⁸ Forster

Grant L.

https://orcid.org/0000-0003-1783-9307

⁹ Reeves

Claire E.

https://orcid.org/0000-0003-4071-1926

⁸ Monks

Paul S.

² Heard

Dwayne E.

https://orcid.org/0000-0002-0357-6238

School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK

School of Chemistry, University of Leicester, University Road, Leicester, LE1 7RH, UK

National Centre for Atmospheric Science, University of Leeds, Leeds, LS2 9JT, UK

School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UK

Research Software Engineering Team, University of Leicester, Leicester, LE1 7RH, UK

Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York, YO10 5DD, UK

National Centre for Atmospheric Science, University of York, York, YO10 5DD, UK

Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia, Norwich, UK

National Centre for Atmospheric Science, University of East Anglia, Norwich, NR4 7TJ, UK

now at: Digital Research Service, University of Nottingham, Nottingham, NG7 2RD, UK

now at: Faculty for Airborne Atmospheric Measurements, Cranfield University, Cranfield, MK43 0AL, UK

now at: Department of Chemistry, York University, Toronto, M3J 1P3, Canada

now at: Ricardo Energy & Environment, Harwell, Oxfordshire, OX11 0QR, UK

11 04 2022

2022 1 53

2022

This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/

This article is available from https://acp.copernicus.org/preprints/acp-2022-207/

The full text article is available as a PDF file from https://acp.copernicus.org/preprints/acp-2022-207/acp-2022-207.pdf

OH, HO2, total and partially-speciated RO2, and OH reactivity (k’OH) 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 k’OH 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.

Natural Environment Research Council

NE/K012029/1

NE/K012169/1

NE/K004069/1