Dependence of Isoprene SOA Yield on the Phase of Ammonium Sulfate Seed Particles

Friday, 19 December 2014
Jenny P S Wong, Alex Lee and Jonathan Abbatt, University of Toronto, Department of Chemistry, Toronto, ON, Canada
Current atmospheric models have difficulty predicting the mass of ambient organic bearing particles, suggesting unidentified formation mechanisms. As well, there is growing evidence that the partitioning of water-soluble organic gases to particle-phase liquid water and their subsequent condensed-phase reactions can form additional SOA to that formed by more traditional mechanisms. While previous studies have investigated the formation of isoprene SOA under a range of relative humidity (RH) conditions, the role of particle-phase liquid water in SOA formation remains unclear. The objective of this work is to investigate the effects of particle-phase liquid water on isoprene SOA yield. SOA was generated from the OH oxidation of isoprene at RH 75% in the presence of either effloresced (i.e. dry) or deliquesced (i.e. wet) ammonium sulfate (AS) particles. Results suggest that SOA yield is enhanced for wet AS seed particles. The effects of particle acidity on SOA formation will be presented as well. These experimental results demonstrate the importance of particle-phase liquid water on the uptake of volatile organic gases and their contributions to SOA formation.