Dept. of Environmental and Biomolecular Systems
Oregon Health & Science University
Predicting the formation of organic particulate matter (OPM) in the atmosphere by absorptive gas/particle (G/P) partitioning requires a knowledge of the identities, atmospheric levels, and physical properties of all condensable species. It is known that a portion of atmospheric OPM samples are comprised of products generated during oxidation of volatile organic compounds. Additionally, initially formed oxidation products may undergo reactions with one another and/or other atmospheric constituents, i.e. "accretion reactions", leading to the formation of high-molecular weight (MW)/low volatility compounds that can form OPM. The proposed mechanism by which oxidation products and other atmospheric constituents (e.g., A and B) may contribute to OPM formation is: Ag + Bg = Cg (accretion), then Cg â Cliq (condensation). Initially, chamber studies focused on accretion reactions as a general mechanism for OPM formation and the potential role of acid-catalysis in increasing OPM formation by this mechanism; more recently, such studies have focused on detection and quantification of accretion products and on the effects of particle acidity and parent compound structure on accretion product formation. However, many uncertainties exist regarding accretion reactions as they may occur in the atmosphere, including identification of specific accretion products and their formation pathways. A general theoretical method has been developed to evaluate thermodynamic favorabilities of accretion reactions, including the extent to which they may contribute to atmospheric OPM. If an accretion reaction is to produce significant OPM, appreciable amounts of the product C must form, and the vapor pressure of C must be relatively low so that a significant proportion of C can condense into the multi-component liquid OPM phase. In considerations of aldehydes, ketones, dialdehydes, methylglyoxal, diketones, carboxylic and dicarboxylic acids, it was concluded that: 1) the types of accretion reactions considered are not favorable for mono- and diketones and ~C5 and lower mono and dialdehydes; 2) aldol condensation of ~C6 and higher mono- and dialdehydes may contribute to atmospheric OPM formation under some circumstances; 3) diol and diololigomer formation from glyoxal, aldol condensation of methylglyoxal, and esterification and amide formation from carboxylic and dicarboxylic acids are thermodynamically favorable, and may contribute significantly to OPM in the atmosphere.
OGI School of Science and Engineering
Barsanti, Kelley Claire, "A general theoretical method for evaluating the formation of high-molecular weight/low-volatility compounds and their contribution to atmospheric organic particulate matter" (2006). Scholar Archive. 6.