Thermodynamics of the formation of atmospheric organic particulate matter by accretion reactions—Part 3: Carboxylic and dicarboxylic acids

The term “accretion reactions” has been used to describe the collection of reactions by which organic compounds can react with one another and/or other atmospheric constituents, forming products of higher-molecular weight (MW) and lower volatility, and thus increasing their tendency to condense [Barsanti, K.B., Pankow, J.F., 2004. Thermodynamics of the formation of atmospheric organic particulate matter by accretion reactions—Part 1: Aldehydes and ketones. Atmospheric Environment 38, 4371–4382; Barsanti, K.B., Pankow, J.F., 2005. Thermodynamics of the formation of atmospheric organic particulate matter by accretion reactions—Part 2: Dialdehydes, methylglyoxal, and diketones. Atmospheric Environment 39, 6597–6607]. Studies have shown that a significant fraction of atmospheric organic particulate matter (OPM) may be comprised of high-MW/low-volatility compounds [e.g., Havers, N., Burpa, P., Lambert, J., Klockow, D., 1998. Spectroscopic characterization of humic-like substances in airborne particulate matter. Journal of Atmospheric Chemistry 29, 45–54], which would be consistent with the occurrence of such accretion reactions in the atmosphere, [e.g., Jang, M., Czoschke, N. M., Lee, S., Kamens, R. M., 2002. Heterogeneous atmospheric organic aerosol production by acid-catalyzed particle-phase reactions. Science 298, 814–817]. However, many uncertainties exist regarding accretion reactions as they may occur in the atmosphere, including identification of those reactions most likely to contribute to OPM.Barsanti and Pankow (2004, 2005) have developed and applied a general theoretical approach to evaluate the thermodynamic favorabilities of accretion reactions, including the extents to which they may be relevant for OPM formation in the atmosphere. That approach is applied here in the consideration of OPM formation by reactions of four mono- and dicarboxylic acids (acetic, malic, maleic, and pinic) to form esters and amides. It was concluded that for all of the acids considered, ester and amide formation are thermodynamically favored under the assumed conditions. For malic, maleic, and pinic acids, and likely for similar mono- and dicarboxylic acids, significant OPM formation may occur via ester and amide formation in the atmosphere when kinetically favorable.