AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Measurements of Oxidized Organic Compounds during SOAS 2013 Using Nitrate Ion Chemical Ionization Coupled with High Resolution Time-of-Flight Mass Spectrometry
PAOLA MASSOLI, Harald Stark, Manjula Canagaratna, Heikki Junninen, Jani Hakala, Roy Lee III Mauldin, Mikael Ehn, Mikko Sipilä, Jordan Krechmer, Joel Kimmel, John Jayne, Jose-Luis Jimenez, Douglas Worsnop, Aerodyne Research, Inc.
Abstract Number: 23 Working Group: Aerosol Chemistry
Abstract We present 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. This technique allows to selectively detect low-volatility oxidized organic molecules (ELVOC) and sulfuric acid via clustering with NO3- and its high order clusters. The capability of making such measurements is important because both sulfuric acid and organic gas molecules have a recognized key role in new particle formation (NPF) processes and formation of secondary organic aerosols (SOA). The HR-ToF-CIMS was deployed during the Southern Oxidant and Aerosol Study (SOAS) at the forest supersite in Centreville, AL, from June 1 to July 15, 2013. The main goal of the SOAS campaign was to investigate the composition and sources of SOA in the Southeast US, where emissions are mainly represented by biogenic volatile organic compounds (BVOC) emissions occasionally mixing with anthropogenic emissions. During SOAS, the HR-ToF-CIMS detected a range of organic ions that based on previous literature could be identified as oxidation products of both isoprene and terpenes. The isoprene-related molecules showed a diurnal cycle with a day time peak, typically after 1500 local time, while the terpene products were higher at night (between 2000 and 0600 local time). Positive Matrix Factorization (PMF) analyses are applied to the dataset to extract additional information on the sources of the observed molecules and interpret the observations through the correlation with gas and particle external tracers. The sensitivity of the measurements to ambient RH is also explored. Finally, the ambient data are compared to laboratory measurements where oxidized organic vapors are produced using a Potential Aerosol Mass (PAM) flow reactor by the OH oxidation of biogenic gas-phase precursors (isoprene, a-pinene) over multiple days of equivalent atmospheric exposure.