An isotopic analysis of ionising radiation as a source of sulphuric acid

摘要

Sulphuric acid is an important factor in aerosol nucleation and growth. Ithas been shown that ions enhance the formation of sulphuric acid aerosols,but the exact mechanism has remained undetermined. Furthermore some studieshave found a deficiency in the sulphuric acid budget, suggesting a missingsource. In this study the production of sulphuric acid from SO through anumber of different pathways is investigated. The production methods arestandard gas phase oxidation by OH radicals produced by ozone photolysis withUV light, liquid phase oxidation by ozone, and gas phase oxidation initiatedby gamma rays. The distributions of stable sulphur isotopes in the productsand substrate were measured using isotope ratio mass spectrometry. Allmethods produced sulphate enriched in S and we find an enrichment factor (δS)of 8.7 ± 0.4‰ (1 standard deviation) for theUV-initiated OH reaction. Only UV light (Hg emission at 253.65 nm) produced aclear non-mass-dependent excess of S. The pattern of isotopicenrichment produced by gamma rays is similar, but not equal, to that producedby aqueous oxidation of SO by ozone. This, combined with the relativeyields of the experiments, suggests a mechanism in which ionising radiationmay lead to hydrated ion clusters that serve as nanoreactors for S(IV) toS(VI) conversion.