10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Formula vs. Structure: Impacts of Isomers on Interpretation, Calibration, and Parameterization of Atmospheric Mass Spectrometric Data
GABRIEL ISAACMAN-VANWERTZ, Bernard Aumont, Manjula Canagaratna, Paola Massoli, John Nowak, Jordan Krechmer, Rachel O'Brien, Jesse Kroll, Douglas Worsnop, Virginia Tech
Abstract Number: 1349 Working Group: Aerosol Chemistry
Abstract Recent advances in field-deployable mass spectrometry of gas- and particle-phase organic compounds have provided unprecedented characterization of atmospheric mixtures. However, while organic carbon across the entire range of atmospheric properties has become measurable by current state-of-the-art tools, many of these instruments identify analytes only by elemental formula with little or no structural information. The appearance of different isomers as the same chemical species (i.e. ion) may critically impact source apportionment, understanding of chemical processes, and instrument calibration. Furthermore, a substantial body of work has generated and utilized empirical parameterizations of molecular properties (e.g. volatility and reactivity) based on elemental formulas, despite these properties having strong structural dependencies. Consequently, it is possible the presence of isomers in ambient samples is a major source of uncertainty in data interpretation due to the lack of structural information provided by many instruments. However, the extent to which (unmeasured) isomers impact current understanding is not well known since no comprehensive effort has been made to catalog the importance of isomers in the atmosphere. We capitalize on a diverse set of published and new isomer-resolved measurements (gas chromatography, liquid chromatography, ion mobility) to answer the fundamental question: “How prevalent are isomers in the atmosphere, and what does this mean for our data?”. We find that molecular formulas typically represent several, and in some cases up to 10, isomers. Calibration and interpretation of gas-phase mass spectrometer data from a suite of biogenic oxidation experiments will be discussed in this context, and atmospherically-relevant structures generated by the GECKO-A model will provide estimates of the uncertainty isomers may introduce into current parametrizations.