Effect of Ammonia on Glyoxal SOA in Inorganic Aqueous Seed Particles

Friday, 19 December 2014: 2:00 PM
Rainer M Volkamer1, Eleanor Waxman1, Alexander Laskin2, Julia Laskin3, Theodore Konstantinos Koenig4, Urs Baltensperger5, Josef Dommen5, Andre S Prevot5, Jay Slowik5, Aurelia Maxut6, Barbara Noziere7, Siyuan Wang1,8 and Jianzhen Yu8, (1)University of Colorado at Boulder, Boulder, CO, United States, (2)Pacific North West National Laboratory, EMSL, Richland, WA, United States, (3)Pacific Northwest National Laboratory, Richland, WA, United States, (4)University of Colorado at Boulder, Department of Chemistry and Biochemistry, Boulder, CO, United States, (5)Paul Scherrer Institute, Villingen, Switzerland, (6)IRCELyon Institut de recherches sur la catalyse et l'environnement de Lyon, Villeurbanne, France, (7)CNRS, Caluire, France, (8)Hong Kong University of Science and Technology, Hong Kong, Hong Kong
Glyoxal (C2H2O2) is a ubiquitous small molecule that is observed in the terrestrial biogenic, urban, marine and arctic atmosphere. It forms secondary organic aerosol (SOA) as a result of multiphase chemical reactions in water. The rate of these reactions is controlled by the effective Henry’s law partitioning coefficient (Heff) which is enhanced in the presence of inorganic salts by up to 3 orders of magnitude (Kampf et al., 2013, ES&T). Aerosol particles are among the most concentrated salt solutions on Earth and the SOA formation rate in aerosol water is strongly modified by this ‘salting-in’ mechanism. We have studied the effect of gas-phase ammonia on the rate of SOA formation in real particles composed of different inorganic salts (sulfate, nitrate, chloride). A series of simulation chamber experiments were conducted at the Paul Scherrer Institut in Switzerland during Summer 2013. The SOA formation rate in experiments with added gas-phase ammonia (NH3) was found to be greatly accelerated compared to experiments without added NH3. Product analysis of particles included online HR-ToF-AMS and offline nano-DESI and LC-MS. We find that imidazole-like oligomer compounds dominate the observed products, rather than high-O/C oligomers containing solely C, H, and O. We further employed isotopically labelled di-substituted 13C glyoxal experiments in order to unambiguously link product formation to glyoxal (and separate it from chamber wall contamination). We present a molecular perspective on the reaction pathways and evaluate the effect of environmental parameters (RH, particle pH, seed chemical composition) on the formation of these imidazole-like oligomer compounds. The implications for SOA formation from photosensitized oxidation chemistry is discussed.