OH and HO₂ chemistry during NAMBLEX: roles of oxygenates, halogen oxides and heterogeneous uptake

R. Sommariva (1) , W. J. Bloss (1) , N. Brough (2) , N. Carslaw (3) , M. Flynn (4) , A.-L. Haggerstone (1) , D. E. Heard (1) , J. R. Hopkins (1) , J. D. Lee (1) , A. C. Lewis (1) , G. Mcfiggans (4) , P. S. Monks (1) , S. A. Penkett (2) , M. J. Pilling (1) , J. M. C. Plane (2) , K. A. Read (1) , A. Saiz-Lopez (2) , A. R. Rickard (1) , P. I. Williams (4)

1 Department of Chemistry
2 School of Environmental Sciences [Norwich]
3 Environment Department
4 SEAES - School of Earth, Atmospheric and Environmental Sciences [Manchester]

Several zero-dimensional box-models with different levels of chemical complexity, based on the Master Chemical Mechanism (MCM), have been used to study the chemistry of OH and HO₂ in a coastal environment in the Northern Hemisphere. The models were constrained to and compared with measurements made during the NAMBLEX campaign (Mace Head, Ireland) in summer 2002.

The base models, which were constrained to measured CO, CH₄ and NMHCs, were able to reproduce [OH] within 25%, but overestimated [HO₂] by about a factor of 2. Agreement was improved when the models were constrained to oxygenated compounds (acetaldehyde, methanol and acetone), highlighting their importance for the radical budget. When the models were constrained to measured halogen monoxides (IO, BrO) and used a more detailed, measurements-based, treatment to describe the heterogeneous uptake, modelled [OH] increased by up to 15% and [HO₂] decreased by up to 30%. The actual impact of halogen monoxides on the modelled concentrations of HO_x was dependant on the uptake coefficients used for HOI, HOBr and HO₂. The best agreement with the measurements was achieved by constraining the model to measured IO and setting ?_HO2=1 and ?_HOI=0.6.

A rate of production and destruction analysis of the models allowed a detailed study of OH and HO₂ chemistry under the conditions encountered during NAMBLEX, showing the importance of oxygenates and of XO (where X=I, Br) as co-reactants for OH and HO₂ and of HOX photolysis as a source for OH.

Domaines: Océan, Atmosphère

R. Sommariva, W. J. Bloss, N. Brough, N. Carslaw, M. Flynn, et al.. OH and HO₂ chemistry during NAMBLEX: roles of oxygenates, halogen oxides and heterogeneous uptake. Atmospheric Chemistry and Physics Discussions, 2005, 5 (6), pp.10947-10996. ⟨hal-00301891⟩