Water-Soluble Atmospheric Organic Matter in Fog: Exact Masses and Chemical Formula Identification by Ultrahigh-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Abstract

The detailed molecular composition of water-soluble atmospheric organic matter (AOM) contained in fog water was studied by use of electrospray ionization ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry. We identified 1368 individual molecular masses in the range of 100-400 Da from negative-ion spectra obtained after reversed-phase extraction with a hydrophilic solid phase sorbent. The detected organic anions are multifunctional with a variety of oxygenated functional groups. We observe organic nitrogen, organic sulfur, and organic nitrogen-sulfur compounds as well as many species with only C, H, and O elemental composition. Analysis of the double bond equivalents (DBE = the number of rings plus the number of double bonds to carbon) suggests that these compound structures range from highly aliphatic to aromatic with DBE values of 1-11. The compounds range in their extent of oxidation with oxygen to carbon ratios from 0.2 to 2 with an average value of 0.43. Several homologous series of compounds and multifunctional oligomers were identified in this AOM. The high extent of homologous series of compounds likely originates from primary components that have become oxidized. The multifunctional oligomers appear to represent atmospheric processing of primary and secondary compounds. The isolated water-soluble components identified here are amphiphilic, meaning that they contain both hydrophilic oxygenated functional groups and hydrophobic aliphatic and aromatic structural moieties. Despite the high number of compounds with very high oxygen content, 60% of assigned chemical formulas have measured organic mass-to-organic carbon ratios <or=2.25 (ranging from 1.25 to 3.5). Because the results reported here are not quantitative, an average ratio cannot be determined.

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

“…3. It is plausible that aqueous nitrate radical chemistry might be a source of oxygenated organic nitrogen compounds measured in fog and rain water, [41,42] although these compounds could also have been formed through gas-phase chemistry. If the nitrate radicals were formed by photolysis in the aqueous phase and if these reactions occur at dilute concentrations, we should see organonitrate products in experimental samples.…”

“…Inorganic nitrate and ammonium are found in atmospheric cloud and fog waters (e.g. ,1 mM-3 mM for NO 3 -and NH 4 þ in fogs), [38][39][40][41] and organic nitrogen species have been measured in California fogs [42] and New Jersey rainwater. [41] Although organic nitrogen is clearly formed through gas-phase chemistry and there is evidence for its formation in aerosols, it could plausibly also form through cloud and fog chemistry.…”

Biogenic, urban, and wildfire influences on the molecular composition of dissolved organic compounds in cloud water

“…Therefore, the DBE calculation does not account for tetravalent and hexavalent S or pentavalent N (Mazzoleni et al, 2010).…”

Fogs and Air Quality on the Southern California Coast

“…Fog samples at CP contained multiple CHOS and CHNOS species derived from biogenic and anthropogenic molecules, some of which have been observed in fog and aerosol samples previously . These species (tentatively) included hydroxybutanoic acid, sulfate ester (C 4 H 8 O 6 S), a methylglyoxal oxidation product (C 6 H 10 O 7 S; Sareen et al, 2010), C 7 H 7 NO 5 S, methylnitrophenol sulfate ester (C 7 H 7 NO 6 S), a limonene oxidation product (C 8 H 14 O 7 S; Surratt et al, 2008;Mazzoleni et al, 2010), C 9 H 14 O 7 S, and C 21 H 15 NO 8 S.…”