Evidence for short SO2 lifetimes in the atmosphere - an in-situ measurement of atmospheric SO2 lifetime using cosmic ray produced sulphur-38

A method for the determination of the in-situ lifetime of atmospheric SO2 has been developed using cosmic ray produced radioactive S(38-isotope). The S(38-isotope)-production rate by cosmic rays and the SO2(38-isotope) radioactivity of atmospheric samples have been measured. The lifetimes of SO2 have been obtained by comparison of the SO2(38-isotope)-concentrations actually measured and modelled concentrations; the modelling takes into account vertical mixing, dry deposition and radioactive decay, but not in-situ conversion into particulate S (horizontal mixing is neglected in the model). The apparent lifetimes determined by the S(38-isotope)-method, ranging between 1/2 and a few h in most cases, are much shorter than lifetimes reported up to now. Lifetimes seem to be strongly influenced by solar radiation. Simple S balance considerations give further evidence for short SO2 lifetimes in the atmosphere. (IFU