H 2 SO 4 formation from the gas-phase reaction of stabilized Criegee Intermediates with SO 2 : Influence of water vapour content and temperature Torsten Berndt a, * , Tuija Jokinen a, b , Mikko Sipilä b , Roy L. Mauldin III b, c , Hartmut Herrmann a , Frank Stratmann a , Heikki Junninen b , Markku Kulmala b a Leibniz-Institute for Tropospheric Research (TROPOS), 4318 Leipzig, Germany b Department of Physics, University of Helsinki, Finland c University of Colorado at Boulder, Boulder, CO, USA highlights  The sCI reactivity towards water vapour is dependent on the sCI structure.  Acetone oxide shows no measurable reaction with water vapour.  Increasing temperature pushes back H 2 SO 4 formation from sCI þ SO 2 . article info Article history: Received 26 August 2013 Received in revised form 24 February 2014 Accepted 27 February 2014 Keywords: Gas-phase ozonolysis Criegee Intermediate Stabilization Atmospheric H 2 SO 4 formation CI-APi-TOF mass spectrometry abstract The importance of gas-phase products from alkene ozonolysis other than OH radicals, most likely sta- bilized Criegee Intermediates (sCI), for the process of atmospheric SO 2 oxidation to H 2 SO 4 has been recently discovered. Subjects of this work are investigations on H 2 SO 4 formation as a function of water vapour content (RH ¼ 2e65%) and temperature (278e343 K) starting from the ozonolysis of trans-2- butene and 2,3-dimethyl-2-butene (TME). H 2 SO 4 production other than via the OH radical reaction was attributed to the reaction of SO 2 with sCI, i.e. acetaldehyde oxide arising from trans-2-butene ozonolysis and acetone oxide from TME. Measurements have been conducted in an atmospheric pres- sure flow tube using NO 3  eCI-APi-TOF mass spectrometry for H 2 SO 4 detection. The sCI yields derived from H 2 SO 4 measurements at 293 K were 0.49  0.22 for acetaldehyde oxide and 0.45  0.20 for acetone oxide. Our findings indicate a H 2 SO 4 yield from sCI þ SO 2 of unity or close to unity. The deduced rate coefficient ratio for the reaction of sCI with H 2 O and SO 2 , k(sCI þ H 2 O)/k(sCI þ SO 2 ), was found to be strongly dependent on the structure of the Criegee Intermediate, for acetaldehyde oxide at 293 K: (8.8  0.4)$10 5 (syn- and anti-conformer in total) and for acetone oxide: <4$10 6 .H 2 SO 4 formation from sCI was pushed back with rising temperature in both reaction systems most probably due to an enhancement of sCI decomposition. The ratio k(dec)/k(sCI þ SO 2 ) increased by a factor of 34 (acetone oxide) increasing the temperature from 278 to 343 K. In the case of acetaldehyde oxide the temperature effect is less pronounced. The relevance of atmospheric H 2 SO 4 formation via sCI þ SO 2 is discussed in view of its dependence on the structure of the Criegee Intermediate. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction It was already found in the seventies that reactive intermediates from alkene ozonolysis (other than OH radicals) are able to oxidize SO 2 under atmospheric conditions forming H 2 SO 4 (Cox and Penkett, 1972). These reactive intermediates are most likely stabi- lized Criegee Intermediates (sCI) (Criegee, 1975). Very recently, it was discovered that the reaction of sCI with SO 2 is surprisingly fast and significantly contributes to atmospheric H 2 SO 4 formation be- sides the well-known process via OH þ SO 2 (Welz et al., 2012; Mauldin et al., 2012). Modelling results, however, call a substan- tial H 2 SO 4 formation from sCI into question and point to a possibly * Corresponding author. E-mail address: berndt@tropos.de (T. Berndt). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv http://dx.doi.org/10.1016/j.atmosenv.2014.02.062 1352-2310/Ó 2014 Elsevier Ltd. All rights reserved. Atmospheric Environment 89 (2014) 603e612