Observed H2SO4 and OH concentrations and their relation to particle nucleation events in marine and rural continental air

High-time resolution measurements of ambient H2SO4 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 H2SO4 molecules contributing to new particle formation can be reasonably estimated for the rural event conditions (on the order of a few 104 molec. cm−3 s−1 or higher) by comparing calculated and measured H2SO4 levels. However, for the coastal marine site simple balance calculations assuming the SO2+OH reaction to be the only source of gaseous H2SO4 resulted in H2SO4 concentrations much lower than observed levels suggesting the presence of an unaccounted major source of H2SO4 in this environment. Other observations at Mace Head indicated a significant suppression of ambient OH concentrations, in particular during a midday particle burst at lo...