Glyoxal uptake on ammonium sulphate seed aerosol: reaction products and reversibility of uptake under dark and irradiated conditions

Abstract

Abstract. Chamber studies of glyoxal uptake onto ammonium sulphate aerosol were performed under dark and irradiated conditions to gain further insight into processes controlling glyoxal uptake onto ambient aerosol. Organic fragments from glyoxal dimers and trimers were observed within the aerosol under dark and irradiated conditions. Glyoxal monomers and oligomers were the dominant organic compounds formed under the conditions of this study; glyoxal oligomer formation and overall organic growth were found to be reversible under dark conditions. Analysis of highresolution time-of-flight aerosol mass spectra provides evidence for irreversible formation of carbon-nitrogen (C-N) compounds in the aerosol. We have identified 1H-imidazole-2-carboxaldehyde as one C-N product. To the authors' knowledge, this is the first time C-N compounds resulting from condensed phase reactions with ammonium sulphate seed have been detected in aerosol. Organosulphates were not detected under dark conditions. However, active photochemistry was found to occur within aerosol during irradiated experiments. Carboxylic acids and organic esters were identified within the aerosol. An organosulphate, which had been previously assigned as glyoxal sulphate in ambient samples and chamber studies of isoprene oxidation, was observed only in the irradiated experiments. Comparison with a laboratory synthesized standard and chemical considerations strongly suggest that this organosulphate is glycolic acid sulphate, an isomer of the previously proposed glyoxal sulphate.Correspondence to: F. N. Keutsch (keutsch@wisc.edu) Our study shows that reversibility of glyoxal uptake should be taken into account in SOA models and also demonstrates the need for further investigation of C-N compound formation and photochemical processes, in particular organosulphate formation.

Glyoxal secondary organic aerosol chemistry: effects of dilute nitrate and ammonium and support for organic radical–radical oligomer formation

“…[21] This suggests that the presence of NH 4 þ at cloud-relevant concentrations will not affect GLY þ OH chemistry. In addition, we found no evidence of the imidazoles reported by Galloway et al [6] by FT-ICR MS in the positive mode.…”

“…[37] In addition, imidazole formation has been detected in (dark) concentrated aldehydeammonium sulfate solutions and chamber experiments. [6,34] Inorganic and organic concentrations are orders of magnitude smaller in clouds and fogs. Although experiments have been performed to examine the effect of dilute (cloud-relevant) concentrations of acidic sulfate on GLY chemistry, [33] to our knowledge the degree to which GLY þ OH chemistry is altered by the presence of cloud-relevant concentrations of nitrate or ammonium has not been examined.…”

“…[32,33] Organic nitrogen and sulfur compounds have been observed to form in highly concentrated aqueous solutions relevant to wet aerosols. [6,[34][35][36][37] Evidence for the photochemical formation of organosulfates from GLY and other aldehydes is provided through studies of bulk sulfate solutions and through smog chamber experiments with ammonium sulfate seed particles and UV irradiation. [6,35,36] Aerosol mimic solutions containing GLY and inorganic ammonium salts have yielded products with carbon-nitrogen bonds in the absence of major atmospheric oxidants (i.e.…”

“…oxalate, glycolate, oligomers, epoxide sulfates and imidazoles). [1][2][3][4][5][6][7][8][9][10][11] As a result, gas-phase followed by aqueous-phase chemistry contributes to secondary organic aerosol (SOA). [12,13] SOA is also formed when semiand low-volatility products of gas-phase chemistry sorb to particulate organic matter [14,15] (here SOA gas is used to denote SOA formed by this latter pathway and SOA aq to denote SOA formed with a contribution from aqueous-phase chemistry).…”

“…oxalate, oligomers, organosulfate and imidazole). [6,8,[32][33][34] Because these compounds are found predominantly in the condensed phase in the atmosphere, aqueous reaction of GLY contributes to SOA aq . [32,33] Organic nitrogen and sulfur compounds have been observed to form in highly concentrated aqueous solutions relevant to wet aerosols.…”