Ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry identification of water-soluble atmospheric organic matter in polluted fog waters (invited)

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 hundreds of individual molecular masses in the range of 100-400 u as negative quasi-molecular ions. In our fog water samples, we found a high degree of complexity across the mass range of 100 to 400 u and in some cases our mass range extended up to 1000 u. The detected negative organic ions were multifunctional compounds which included C, H, N, O, and S elements. We observed organic nitrogen (CHNO), organic sulfur (CHOS), and organic nitrooxy-sulfate compounds (CHNOS) as well as many masses with only CHO 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 ranged in their extent of oxidation with oxygen to carbon ratios from 0.2 to 2 with an average value of 0.43. Several CH2 and C3H4O2 series of compounds were identified in this AOM. The high extent of CH2 homologous series of compounds likely originates from primary components that have become oxidized. Over 400 C3H4O2 series (sometimes referred to as oligomers) were also found. Overall, approximately 80% of the CHO and CHNO compounds can be linked through C3H4O2 series. The series appear to represent atmospheric processing of primary and secondary compounds. However, they may also result coincidentally by atomic valence of these elements and the very high number of ions detected in these AOM samples. In general, the isolated water-soluble components identified here are amphiphilic, thus they contain both hydrophilic oxygenated functional groups and hydrophobic aliphatic and aromatic structural moieties. Results and implications from our analysis of several samples of polluted fog water will be presented