ABSTRACT
Aqueous-phase photochemical oxidation reactions in clouds are known to play an important role in the overall chemistry of the troposphere. Concerns about acid deposition have fueled much interest in these processes. The atmospheric oxidation of sulfur dioxide occurs largely within cloud droplets. This chapter discusses the formation and measured steady-state concentrations of peroxyl radicals and singlet molecular oxygen, O2, in illuminated authentic cloud water samples. The experiments performed demonstrate that aqueous-phase photochemical production of these oxidants can lead to concentrations in the aqueous phase that equal or exceed concentrations predicted by atmospheric models that are based primarily upon gas-to-drop partitioning as the source for aqueous-phase oxidants. Measurements of the Ultraviolet-visible spectra for blanks in which pure deionized/distilled water was used to rinse all surfaces of cloud water collectors and storage containers did not show the characteristic absorption typical of the cloud water samples.
