Experimental and theoretical study of S(IV)/S(VI) ratio in rain and cloud events

Production of atmospheric sulfate from SO_2 emitted into the troposphere is the key question we have to answer for assessing main problems like acid rain, forest decline and negative climate forcing which is believed to counteract the green house effect. About one decade ago many researchers agreed that sulfate formation occurs dominantly (80-90 %) via the aqueous phase chemical transformation, where the SO_2 dissociation is the first step. However, there is still a high uncertainty on the amount of sulfite (dissolved SO_2) being oxidized and on that removed by wet deposition in the reduced form S(IV) (sulfite). This important question, whose answer gives climate modellers an essential input on the percentage of emitted SO_2 converted into sulfate, was the aim of this work. This work presents experimental and theoretical results from studies of the ratio sulfite/sulfate in rainwater and cloudwater to assess the contribution of S(IV) to the total sulfur amount in the aqueous phase. Our findings suggest that considerable part of emitted SO_2 will not be transformed to sulfate especially in the sub-cloud layer. Therefore, the production of climate affecting sulfate aerosol via aqueous phase transformation of dissolved SO_2 is more limited than believed by climate modellers.SIGLEAvailable from: http://www.ub.tu-cottbus.de/hss/diss/fak4/tiankunze/pdf/disstiankunze.pdf / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman