Abstract.Concurrent measurements of ultra-fine (r<5 nm)

Abstract. An observationally constrained box model has been constructed in order to investigate the chemistry of the marine boundary layer at Mace Head, a remote location on the west coast of Ireland. The primary aim of the model is to reproduce concentrations of the hydroxyl (OH) and hydroperoxy (HO2) radicals measured by an in situ fluorescence assay by gas expansion (

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[1] Measurements of the OH radical during winter show that noon-time concentrations at an urban site in Birmingham are only a factor of 2 less than during summer at the same site, despite a factor of 15 reduction in OH production from the photolysis of ozone. Noon-time concentrations of HO 2 were similar for summer and winter. These high winter concentrations are quantitatively reproduced by a detailed box-model, showing that the winter radical pool (OH, HO 2 , RO 2 ) is sustained by reactions of unsaturated hydrocarbons with ozone and by the photolysis of carbonyls. The high OH concentrations show there is significant chemical processing of volatile organic compounds (VOCs) in winter at mid-to-high latitudes in the northern hemisphere where emissions are high.

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