A13E-0386
Laboratory and Ambient Measurements of Oxidized Organic Compounds in the Gas Phase Using Nitrate Ion Chemical Ionization Coupled with High Resolution Time-of-Flight Mass Spectrometry

Monday, 14 December 2015
Poster Hall (Moscone South)
Paola Massoli1, Harald Stark1,2, Manjula R Canagaratna1, Jordan Krechmer3, Andrew T Lambe1, Gabriel A Isaacman-VanWertz4, John B Nowak1, Joel Kimmel5, Jesse H Kroll4, John Toulson Jayne6 and Douglas R Worsnop1, (1)Aerodyne Research Inc., Billerica, MA, United States, (2)Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (3)University of Colorado at Boulder, Boulder, CO, United States, (4)Massachusetts Institute of Technology, Cambridge, MA, United States, (5)Tofwerk AG, Thun, Switzerland, (6)Aerodyne Research Inc, Billerica, MA, United States
Abstract:
Chemical Ionization Mass Spectrometry (CIMS) is a widely used technique for molecular level characterization of inorganic and organic gas phase species. Here we present laboratory and ambient measurements of gaseous organic compounds by means of a High Resolution Time-of-Flight Chemical Ionization Mass Spectrometry (HR-ToF-CIMS) using nitrate ion (NO3-) chemistry, which recently has proven capable of selectively detecting oxidized organic molecules in the gas-phase via clustering with NO3- and its high order clusters. Such low and extremely low volatility organic compounds (LVOC, ELVOC) have an important role in particulate phase chemistry and formation of secondary organic aerosol (SOA).

The HR-ToF-CIMS was deployed during the Southern Oxidant and Aerosol Study (SOAS) at the forest site in Centreville, AL (June 1 - July 15, 2013), where emissions were dominated by biogenic volatile organic compounds (BVOC), occasionally mixing with anthropogenic emissions. During SOAS, the HR-ToF-CIMS detected oxidation products of both isoprene (typically C5 LVOC) and terpenes (typically C10 ELVOC). The isoprene-related LVOC showed a diurnal cycle with a day time peak, while two groups of terpene ELVOC were identified, one peaking at night and one peaking during the day. Positive Matrix Factorization (PMF) analyses are applied to the dataset to further interpret these observations. The effect of anthropogenic pollution on the biogenic-dominated environment was also investigated during periods of elevated nitrous and sulfur dioxide levels. To further aid in interpretation of the SOAS dataset, oxidized organic molecules were produced via OH and O3 initiated oxidation of biogenic gas-phase precursors in targeted laboratory studies and detected using the HR-ToF-CIMS. Spectra were obtained in these studies over a range of simulated atmospheric conditions.

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