1. Radical chemistry and ozone production at a UK coastal receptor site.
- Author
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Woodward-Massey, Robert, Sommariva, Roberto, Whalley, Lisa K., Cryer, Danny R., Ingham, Trevor, Bloss, William J., Ball, Stephen M., Cox, Sam, Lee, James D., Reed, Chris P., Crilley, Leigh R., Kramer, Louisa J., Bandy, Brian J., Forster, Grant L., Reeves, Claire E., Monks, Paul S., and Heard, Dwayne E.
- Subjects
RADICALS (Chemistry) ,PEROXY radicals ,BUDGET ,MEDIAN (Mathematics) ,METROPOLITAN areas ,OZONE ,SEISMIC anisotropy - Abstract
OH, HO 2 , total and partially speciated RO 2 , 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, HO 2 and total RO 2 radical concentrations were in the range 2.6–17 × 10 6 , 0.75–4.2 × 10 8 and 2.3–8.0 × 10 8 molec. cm -3 , respectively. kOH′ 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) and that over major urban conurbations such as London (SW sector). A box model using the Master Chemical Mechanism (MCMv3.3.1) was in reasonable agreement with the OH measurements, but it overpredicted HO 2 observations in NW–SE air in the afternoon by a factor of ∼ 2–3, although slightly better agreement was found for HO 2 in SW air (factor of ∼ 1.4–2.0 underprediction). The box model severely underpredicted total RO 2 observations in both NW–SE and SW air by factors of ∼ 8–9 on average. Measured radical and kOH′ levels and measurement–model ratios displayed strong dependences on NO mixing ratios, with the results suggesting that peroxy radical chemistry is not well understood under high-NO x conditions. The simultaneous measurement of OH, HO 2 , total RO 2 and kOH′ was used to derive experimental (i.e. observationally determined) budgets for all radical species as well as total RO x (i.e. OH + HO 2 + RO 2). In NW–SE air, the RO x budget could be closed during the daytime within experimental uncertainty, but the rate of OH destruction exceeded the rate of OH production, and the rate of HO 2 production greatly exceeded the rate of HO 2 destruction, while the opposite was true for RO 2. In SW air, the RO x budget analysis indicated missing daytime RO x sources, but the OH budget was balanced, and the same imbalances were found with the HO 2 and RO 2 budgets as in NW–SE air. For HO 2 and RO 2 , the budget imbalances were most severe at high-NO mixing ratios, and the best agreement between HO 2 and RO 2 rates of production and destruction rates was found when the RO 2 + NO rate coefficient was reduced by a factor of 5. 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 2 σ) in SW air. The rate of in situ ozone production (P (O x)) was calculated from observations of RO x , NO and NO 2 and compared to that calculated from MCM-modelled radical concentrations. The MCM-calculated P (O x) significantly underpredicted the measurement-calculated P (O x) in the morning, and the degree of underprediction was found to scale with NO. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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