RUI: Secondary Organic Aerosol Formation by Cloud Processing of Alpha-Dicarbonyl and Amine Compounds

University Of San Diego, San Diego CA

Investigators

Abstract

Recent field measurements have shown that there are large, sustained, unidentified sources of secondary organic aerosol (SOA). The alpha-dicarbonyl compounds glyoxal and methylglyoxal are receiving increasing scrutiny as potential SOA sources because of their anthropogenic and biogenic precursors, their efficient uptake by atmospheric water droplets and liquid aerosol particles, and their oligomer-forming potential. Recent work shows that the key to aqueous phase alpha-dicarbonyl reactivity is dehydration followed by nucleophilic attack. The nucleophiles methylamine and several amino acids have been identified in cloud- and fog-water droplets in the atmosphere in micromolar concentrations similar to the alpha-dicarbonyl compounds. These nucleophiles have been identified in preliminary experiments as efficient reaction partners with glyoxal and methylglyoxal, forming products upon drying that irreversibly alter gas-particle partitioning of the reactants, even when re-dissolved. The goal of this research is to characterize these reactions and determine their reaction products, measure the reaction kinetics under realistic conditions, and thereby determine the atmospheric significance of these reactions in forming SOA and oligomeric material via cloud and aerosol processing. The reactions will be studied by several methods. First, scanning mobility particle sizing studies of drying monodispersed cloud droplets will determine the extent of reaction under a range of atmospheric conditions and the effect of reactions on particle volatility, off-gassing, and subsequent cloud processing cycles. Second, bulk ESI-MS and NMR studies on aqueous solutions that have been dried and re-dissolved to simulate cloud processing will be used to chemically characterize reaction products and determine reaction pathways. Third, aerosol mass spectrometric (AMS) analysis of particles produced by simulated cloud processing and by direct aerosol phase reactions will determine if bulk phase reaction products and pathways are applicable under atmospheric conditions. Finally, temperature dependent reaction kinetics will be measured by NMR. Information gained by these experiments will determine the atmospheric significance of alpha-dicarbonyl + amine reactions. Airborne particles influence climate, degrade visibility, and impact human health. The results will help improve atmospheric models used to understand the origin of organic aerosols. These models are widely used to assess the potential effects of aerosols on global climate, regional visibility, and air quality, which are all important societal problems. The project will also support the education of a number of undergraduate students.