Molecular Characterization of Organic Aerosol Using Nanospray Desorption/Electrospray Ionization Mass Spectrometry: CalNex 2010 field study
O'Brien RE, A Laskin, J Laskin, S Liu, R Weber, L Russell, and AH Goldstein. 2013. "Molecular Characterization of Organic Aerosol Using Nanospray Desorption/Electrospray Ionization Mass Spectrometry: CalNex 2010 field study." Atmospheric Environment 68:265-272. doi:10.1016/j.atmosenv.2012.11.056
Aerosol samples from the CalNex 2010 field study were analyzed using high resolution mass spectrometry (HR-MS) coupled to a nanospray-desorption/electrospray ionization (nano-DESI) source. The samples were collected in Bakersfield, CA on June 22-23, 2010. The chemical formulas of over 1300 unique molecular species were detected in the mass range of 50-800 m/z. Our analysis focused on identification of two main groups: compounds containing only carbon, hydrogen, and oxygen (CHO only), and nitrogen-containing organic compounds (NOC). The NOC accounted for 35% (by number) of the compounds observed in the afternoon, and for 59% in the early morning samples. By comparing plausible reactant-product pairs, we propose that over 50% of the NOC in each sample could have been formed through reactions transforming carbonyls into imines. The CHO only compounds were dominant in the afternoon suggesting a photochemical source. The average O:C ratios of all observed compounds were fairly consistent throughout the day, ranging from 0.34 in the early morning to 0.37 at night. We conclude that both photooxidation and ammonia chemistry play important roles in forming the compounds observed in this mixed urban-rural environment.