Observed H[sub 2]SO[sub 4] and OH concentrations and their relation to particle nucleation events in marine and rural continental air

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Abstract
High-time resolution measurements of ambient H 2 SO 4 and OH concentrations were made in conjunction with particle nucleation events observed at a coastal marine (Mace Head, Ireland) and a rural continental site (Hohenpeissenberg, Germany). Strong nucleation events occurred on a daily basis at Mace Head but much less frequently at Hohenpeissenberg. The potential flux of H 2 SO 4 molecules contributing to new particle formation can be reasonably estimated for the rural event conditions (on the order of a few 10 4 molec. cm −3 s −1 or higher) by comparing calculated and measured H 2 SO 4 levels. However, for the coastal marine site simple balance calculations assuming the SO 2 +OH reaction to be the only source of gaseous H 2 SO 4 resulted in H 2 SO 4 concentrations much lower than observed levels suggesting the presence of an unaccounted major source of H 2 SO 4 in this environment. Other observations at Mace Head indicated a significant suppression of ambient OH concentrations, in particular during a midday particle burst at low tide. However, no general correlations were observed between tidal cycles and H 2 SO 4 and OH diel variations. It is concluded that nucleation events observed in both environments are related to quite different aerosol gaseous precursor chemistry.

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