Atmospheric Environment 36 (2002) 4627–4634 Kinetics and mechanism of the oxidation of dimethylsulfoxide (DMSO) and methanesulfinate (MSI  )byOHradicalsin aqueous medium H. Bardouki a , M. Barcellos da Rosa b , N. Mihalopoulos a, *, W.-U. Palm c , C. Zetzsch b a Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, P.O. Box 1470, 71409 Heraklion, Greece b Fraunhofer-Institut f . ur Toxikologie und Aerosolforschung, Nikolai-Fuchs-Strasse 1, 30625 Hannover, Germany c University of L . uneburg, Scharnhorststrasse 1, 21335 L . uneburg, Germany Received 28 January 2002; received in revised form 14 June 2002; accepted 26 June 2002 Abstract Kinetics and product distribution of the reaction of dimethylsulfoxide (DMSO) and methanesulfinate (MSI  ) with OHradicalsandH 2 O 2 intheaqueousphasearereportedinthiswork.DMSOisfoundtobeverystableinpurewater or in solutions containing H 2 O 2 . On the other hand, it reacts very rapidly (k ¼ 4:5  10 9 M 1 s 1 ) with OH radicals. MSI  has been identified as the main intermediate product, while methanesulfonate (MS  ) and sulfate were the final productsduetotheveryfastreactionofMSI  withOHradicals(k ¼ 1:2  10 10 M 1 s 1 ).MS  hasbeenidentifiedas the major end product (yield higher than 95%) of both DMSO and MSI  reactions by OH radicals in aqueous solutions.Thepotentialimplicationsofthesereactionsforthebiogenicsulfurcycleintheatmospherearepresentedand discussed. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Sulfur cycle; DMS; DMSO; MSIA; MSA; OH; Photo-oxidation; Heterogeneous reactions 1. Introduction Recent laboratory studies demonstrated that di- methylsulfoxide (DMSO) is an important intermediate of the OH-initiated atmospheric oxidation of dimethyl sulfide(DMS)throughtheadditionchannel,withayield thataccountsforapproximately30%at251Candcould be as high as 70% at low temperatures (Barnes et al., 1994,1996;Hynesetal.,1986).Itwasalsoproposedthat thereactionofDMSwithXOradicals(mainlyBrO)will exclusively lead to DMSO formation (Barnes et al., 1991; Toumi, 1994; Ingham et al., 1999). In the atmosphere, DMSO is expected to undergo homoge- neous (reaction with OH radicals) and heterogeneous reactions during the uptake by an aerosol and/or cloud droplet (Watts et al., 1990). The gas phase reaction of DMSOwithOHradicalshasbeenstudiedbyHynesand Wine (1996) and Urbanski et al. (1998), reporting rate constant of 9  10 11 cm 3 molecule 1 s 1 with a corre- spondinglifetimeofDMSOoftheorderofafewhours. Urbanski et al. (1998) proposed that methanesulfinic acid(MSIA)couldbethemainoxidationproductwitha nearunityyield.Recently,Arseneetal.(2001)confirmed the hypothesis of Urbanski et al. (1998) by detecting MSIAinveryhighyields(closetounity)duringtheOH- radical initiated oxidation of DMSO. Since both DMSO and MSIA are highly water soluble (Watts and Brimblecomble, 1987; De Bruyn etal.,1994)heterogeneousreactionsareexpectedtoplay an important role in determining the fate of both compounds in the atmosphere. Field measurements *Corresponding author. Tel.: +30-810-393-662; fax: +30- 810-393-601. E-mail address: mihalo@chemistry.uoc.gr (N. Mihalopoulos). 1352-2310/02/$-see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S1352-2310(02)00460-0