Identification of atmospheric organic matter in fog water: Exact masses, empirical formulas, and structural insights
Aqueous processing of organic matter by clouds and fogs may significantly alter aerosol-climate properties. Heterogeneous chemical reactions that serve to promote oxidation of apolar primary emission components may result in an increase of hydrophilic organic compounds, while reactions that serve to promote oligomerization and/or formation of larger components, such as HULIS, may result in a decrease. Since aerosol organic matter is very complex and its identity is not well understood, we chose to study the detailed molecular composition of atmospheric organic matter (AOM) of polluted fogs by ultra-high resolution FT-Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). In all of our analyses, we found a high degree of complexity across the mass range of 100 to 400 u and in some of our analyses we observed our mass range to extend up to 1000 u. The detected negative organic ions were multifunctional compounds which include 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 atomic valances by double bond equivalents (DBE) calculations suggests that these compound structures range from highly aliphatic to aromatic with DBE values of 1-11, suggesting a wide variety of precursor compounds with variable oxidation states. This resulted in a high degree of complexity in the low mass range which was greatly reduced by data filtering strategies that group assigned formulas into homologous series and oligomeric series with increasing chain lengths. The AOM oligomeric series with formula differences of C3H4O2 are very likely due to an aqueous esterification reaction, originally suggested by Altieri et al., 2008. We found over 400 oligomer series in our dataset, representing approximately 80% of the CHO and CHNO compounds combined. A very high number of homologous series of compounds and polyfunctional oligomers were found in this dataset, suggesting that these compounds are amphiphilic, meaning that they contain both hydrophilic and hydrophobic structural aspects. Thus, the role of the AOM identified organic compounds with respect to aerosol-climate properties is quite complex. Altieri, K. E., S. P. Seitzinger, A. G. Carlton, B. J. Turpin, G. C. Klein and A. G. Marshall (2008). "Oligomers formed through in-cloud methylglyoxal reactions: Chemical composition, properties, and mechanisms investigated by ultra-high resolution FT-ICR mass spectrometry." Atmospheric Environment 42(7): 1476-1490.
Fall Meeting 2009
Mazzoleni, Lynn and Collett Jr., Jeffrey L., "Identification of atmospheric organic matter in fog water: Exact masses, empirical formulas, and structural insights" (2009). Department of Chemistry Publications. 53.