ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-10-12371-2010 Glyoxal processing outside clouds: towards a kinetic modeling framework of secondary organic aerosol formation in aqueous particles Ervens B. 1 2 Volkamer R. 1 3 Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA Department of Biochemistry and Chemistry, University of Colorado, Boulder, CO, USA 11 05 2010 10 5 12371 12431 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/10/12371/2010/acpd-10-12371-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/10/12371/2010/acpd-10-12371-2010.pdf

This study presents a modeling framework based on laboratory data to describe the kinetics of glyoxal reactions in aqueous aerosol particles that form secondary organic aerosol (SOA). Recent laboratory results on glyoxal reactions are reviewed and a consistent set of reaction rate constants is derived that captures the kinetics of glyoxal hydration and subsequent reversible and irreversible reactions in aqueous inorganic and water-soluble organic aerosol seeds to form (a) oligomers, (b) nitrogen-containing products, (c) photochemical oxidation products with high molecular weight. These additional aqueous phase processes enhance the SOA formation rate in particles compared to cloud droplets and yield two to three orders of magnitude more SOA than predicted based on reaction schemes for dilute aqueous phase (cloud) chemistry. <br><br> The application of this new module in a chemical box model demonstrates that both the time scale to reach aqueous phase equilibria and the choice of rate constants of irreversible reactions have a pronounced effect on the atmospheric relevance of SOA formation from glyoxal. During day time a photochemical (most likely radical-initiated) process is the major SOA formation pathway forming ~5 μg m<sup>&minus;3</sup> SOA over 12 h (assuming a constant glyoxal mixing ratio of 300 ppt). During night time, reactions of nitrogen-containing compounds (ammonium, amines, amino acids) contribute most to the predicted SOA mass; however, the absolute predicted SOA masses are reduced by an order of magnitude as compared to day time production. The contribution of the ammonium reaction significantly increases in moderately acidic or neutral particles (5&lt;pH&lt;7). Reversible glyoxal oligomerization, parameterized by an equilibrium constant <i>K</i><sub>olig</sub>=1000 (in ammonium sulfate solution), contributes &lt;1% to total predicted SOA masses at any time. <br><br> Sensitivity tests reveal five parameters that strongly affect the predicted SOA mass from glyoxal: (1) time scales to reach equilibrium states (as opposed to assuming instantaneous equilibrium), (2) particle pH, (3) chemical composition of the bulk aerosol, (4) particle surface composition, and (5) particle liquid water content that is mostly determined by the amount and hygroscopicity of aerosol mass and to a lesser extent by the ambient relative humidity. <br><br> Glyoxal serves as an example molecule, and the conclusions about SOA formation in aqueous particles can serve for comparative studies also of other molecules that form SOA as the result of multiphase chemical processing in aerosol water. This SOA source is currently underrepresented in atmospheric models; if included it is likely to bring SOA predictions (mass and O/C ratio) into better agreement with field observations.

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