Aqueous phase oxidation of sulphur dioxide by ozone in cloud droplets

C R Hoyle,A Amorim,N Höppel,J Kirkby,M Gysel,Carla Frege ,Sebastian Ehrhart ,Markku Kulmala ,Mario Simon ,Federico Bianchi ,António Tomé ,Chao Yan ,Imad El Haddad ,Gerhard Steiner ,Joachim Curtius ,Paul M Winkler ,Jasmin Tröstl ,Richard C Flagan ,J S Craven ,Armin Hansel ,Alexander L Vogel ,Leonid Nichman ,Emma Järvinen ,Douglas R Worsnop ,António Dias ,Jonathan Duplissy ,Joel C Corbin ,Harald Saathoff ,Christina Williamson ,R J Wagner ,Anne-Kathrin Bernhammer ,Andrea C Wagner ,Rainer Volkamer ,Neil M Donahue ,Josef Dommen ,Thomas Bjerring Kristensen ,Andrê S H Prévôt ,Hamish Gordon ,Jay G Slowik ,Frank Stratmann ,Martin Gallagher ,S Coburn ,Ottmar Möhler ,Tamara Pinterich ,Claudia Fuchs ,Anthony S Wexler ,Martin Breitenlechner ,Martin Heinritzi ,Ugo Molteni ,Urs Baltensperger

doi:10.5194/acp-16-1693-2016

Abstract

Abstract. The growth of aerosol due to the aqueous phase oxidation of sulfur dioxide by ozone was measured in laboratory-generated clouds created in the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN). Experiments were performed at 10 and −10 °C, on acidic (sulfuric acid) and on partially to fully neutralised (ammonium sulfate) seed aerosol. Clouds were generated by performing an adiabatic expansion – pressurising the chamber to 220 hPa above atmospheric pressure, and then rapidly releasing the excess pressure, resulting in a cooling, condensation of water on the aerosol and a cloud lifetime of approximately 6 min. A model was developed to compare the observed aerosol growth with that predicted using oxidation rate constants previously measured in bulk solutions. The model captured the measured aerosol growth very well for experiments performed at 10 and −10 °C, indicating that, in contrast to some previous studies, the oxidation rates of SO2 in a dispersed aqueous system can be well represented by using accepted rate constants, based on bulk measurements. To the best of our knowledge, these are the first laboratory-based measurements of aqueous phase oxidation in a dispersed, super-cooled population of droplets. The measurements are therefore important in confirming that the extrapolation of currently accepted reaction rate constants to temperatures below 0 °C is correct.

Highlights

Sulphur dioxide is an important tropospheric species, influencing air quality as well as the acidity of precipitation
The number of modelled cloud droplets is compared with the number measured by the WELAS, in Fig. 6, for several of the CLOUD9 experiments
The liquid water content (LWC) calculated from the WELAS data is sometimes lower than the LWC derived from the SIMONE, tuneable diode laser (TDL) and MBW data, which may explain part of the discrepancy between modelled and WELAS-measured droplet numbers

Summary

Introduction

Sulphur dioxide is an important tropospheric species, influencing air quality as well as the acidity of precipitation (and that of soil, lakes and rivers). It influences climate directly and indirectly through its oxidation to sulphate and subsequent role in atmospheric new particle formation Global anthropogenic emissions of SO2 around the year 1990 were estimated to be approximately 73 Tg S yr−1 (Rodhe, 1999), more than twice the total sulphur emissions from natural sources. The ratio of anthropogenic to natural emissions can be higher than 10. Air quality legislation in Europe and the USA has led to a significant decline in industrial emissions of SO2 in the last couple of decades, emissions from Asia and developing countries in other locations are increasing (Forster et al, 2007)

Methods

Results

Conclusion