Articles | Volume 15, issue 16
Atmos. Chem. Phys., 15, 9521–9536, 2015
Atmos. Chem. Phys., 15, 9521–9536, 2015

Research article 26 Aug 2015

Research article | 26 Aug 2015

Atmospheric isoprene ozonolysis: impacts of stabilised Criegee intermediate reactions with SO2, H2O and dimethyl sulfide

M. J. Newland1,a, A. R. Rickard2,3, L. Vereecken4, A. Muñoz5, M. Ródenas5, and W. J. Bloss1 M. J. Newland et al.
  • 1University of Birmingham, School of Geography, Earth and Environmental Sciences, Birmingham, UK
  • 2National Centre for Atmospheric Science (NCAS), University of York, York, UK
  • 3Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York, UK
  • 4Max Planck Institute for Chemistry, Atmospheric Sciences, J.-J.-Becher-Weg 27, Mainz, Germany
  • 5Instituto Universitario CEAM-UMH, EUPHORE Laboratories, Avda/Charles R. Darwin, Parque Tecnologico, Valencia, Spain
  • anow at: University of East Anglia, School of Environmental Sciences, Norwich, UK

Abstract. Isoprene is the dominant global biogenic volatile organic compound (VOC) emission. Reactions of isoprene with ozone are known to form stabilised Criegee intermediates (SCIs), which have recently been shown to be potentially important oxidants for SO2 and NO2 in the atmosphere; however the significance of this chemistry for SO2 processing (affecting sulfate aerosol) and NO2 processing (affecting NOx levels) depends critically upon the fate of the SCIs with respect to reaction with water and decomposition. Here, we have investigated the removal of SO2 in the presence of isoprene and ozone, as a function of humidity, under atmospheric boundary layer conditions. The SO2 removal displays a clear dependence on relative humidity, confirming a significant reaction for isoprene-derived SCIs with H2O. Under excess SO2 conditions, the total isoprene ozonolysis SCI yield was calculated to be 0.56 (±0.03). The observed SO2 removal kinetics are consistent with a relative rate constant, k(SCI + H2O) / k(SCI + SO2), of 3.1 (±0.5) × 10−5 for isoprene-derived SCIs. The relative rate constant for k(SCI decomposition) / k(SCI+SO2) is 3.0 (±3.2) × 1011 cm−3. Uncertainties are ±2σ and represent combined systematic and precision components. These kinetic parameters are based on the simplification that a single SCI species is formed in isoprene ozonolysis, an approximation which describes the results well across the full range of experimental conditions. Our data indicate that isoprene-derived SCIs are unlikely to make a substantial contribution to gas-phase SO2 oxidation in the troposphere. We also present results from an analogous set of experiments, which show a clear dependence of SO2 removal in the isoprene–ozone system as a function of dimethyl sulfide concentration. We propose that this behaviour arises from a rapid reaction between isoprene-derived SCIs and dimethyl sulfide (DMS); the observed SO2 removal kinetics are consistent with a relative rate constant, k(SCI + DMS) / k(SCI + SO2), of 3.5 (±1.8). This result suggests that SCIs may contribute to the oxidation of DMS in the atmosphere and that this process could therefore influence new particle formation in regions impacted by emissions of unsaturated hydrocarbons and DMS.

Short summary
Stabilised Criegee intermediates (SCIs) are formed through alkene-ozone reactions, which occur throughout the atmospheric boundary layer. Recent direct laboratory studies have shown that SCI react rapidly with SO2, NO2 and other trace gases, affecting air quality and climate. We present experimental data from the EUPHORE atmospheric simulation chamber, in which we determine the effects of the ozonolysis of isoprene, on the oxidation of SO2 as a function of H2O and dimethyl sulfide concentration.
Final-revised paper