Investigating the Tropospheric Chemistry of Acetic Acid Using the Global 3‐D Chemistry Transport Model, STOCHEM‐CRI

Abstract

Acetic acid (CH3COOH) is one of the most abundant carboxylic acids in the troposphere. In the study, the tropospheric chemistry of CH3COOH is investigated using the 3‐D global chemistry transport model, STOCHEM‐CRI. The highest mixing ratios of surface CH3COOH are found in the tropics by as much as 1.6 ppb in South America. The model predicts the seasonality of CH3COOH reasonably well and correlates with some surface and flight measurement sites, but the model drastically underpredicts levels in urban and midlatitudinal regions. The possible reasons for the underprediction are discussed. The simulations show that the lifetime and global burden of CH3COOH are 1.6–1.8 days and 0.45–0.61 Tg, respectively. The reactions of the peroxyacetyl radical (CH3CO3) with the hydroperoxyl radical (HO2) and other organic peroxy radicals (RO2) are found to be the principal sources of tropospheric CH3COOH in the model, but the model‐measurement discrepancies suggest the possible unknown or underestimated sources which can contribute large fractions of the CH3COOH burden. The major sinks of CH3COOH in the troposphere are wet deposition, dry deposition, and OH loss. However, the reaction of CH3COOH with Criegee intermediates is proposed to be a potentially significant chemical loss process of tropospheric CH3COOH that has not been previously accounted for in global modeling studies. Inclusion of this loss process reduces the tropospheric CH3COOH level significantly which can give even larger discrepancies between model and measurement data, suggesting that the emissions inventory and the chemical production sources of CH3COOH are underpredicted even more so in current global models.

Criegee intermediates and their impacts on the troposphere

“…Further study has shown that the oxidation of SO2 by sCIs can rival the OH oxidation pathway in heavily polluted urban environments, 42 accounting for as much as 33-46% of H2SO4 production at ground level. 99 Recent direct kinetic studies of the reaction of Criegee intermediates with organic acids have identified rate coefficients that are substantially higher, [73][74][75]100 than previous estimates based on theoretical calculations and/or end-product analysis (see 75,104 shows that loss of acids by sCI exceeds 60% of their total loss in South America, South…”

Reaction of Perfluorooctanoic Acid with Criegee Intermediates and Implications for the Atmospheric Fate of Perfluorocarboxylic Acids

“…ranging from zero to 6.0 × 10 5 , with average of 1.5 × 10 4 cm -3 , are estimated in our model study. 5,27 The global distribution of the lifetime of PFOA with respect to the loss by reaction with S.C.I. and the global reduction in lifetime factor of PFOA ((loss by OH + deposition loss)/(loss by OH + deposition loss + loss by S.C.I.)…”

“…It has been shown previously that reaction with Criegee Intermediates is an important gas-phase atmospheric fate of trifluoroacetic acid 2 and other organic acids. [3][4][5] We extend this work by reporting a study of the longer-chain member of the series perfluorooctanoic acid (PFOA; C7F15COOH).…”

Global modeling of cloudwater acidity, rainwater acidity, and acid inputs to ecosystems

“…They are present in the atmosphere at comparable concentrations (Talbot et al, 1997) but HCOOH is more important for contributing to acidity because of its higher Henry's law solubility and lower pKa. Sources of these acids include secondary production from VOC oxidation and direct emissions from biomass burning, fossil-fuels, soils, and vegetation (Khare et al, 1999), but these are poorly understood and models greatly underestimate atmospheric concentrations (Paulot et al, 2011;Stavrakou et al, 2012;Millet et al, 2015;Khan et al, 2018). Here we use the previous GEOS-Chem HCOOH simulation by Millet et al (2015) which scales up the biogenic emissions from the MEGAN inventory (Guenther et al, 2012) in order to fit atmospheric observations over the US.…”