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Atmos. Chem. Phys. Discuss., 12, 5389-5423, 2012
www.atmos-chem-phys-discuss.net/12/5389/2012/
doi:10.5194/acpd-12-5389-2012
© Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.
 
20 Feb 2012
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). A final paper in ACP is not foreseen.
Quantification of diesel exhaust gas phase organics by a thermal desorption proton transfer reaction mass spectrometer
M. H. Erickson, H. W. Wallace, and B. T. Jobson
Laboratory for Atmospheric Research, Washington State University, Pullman, WA, USA

Abstract. A new approach was developed to measure the total abundance of long chain alkanes (C12 and above) in urban air using thermal desorption with a proton transfer reaction mass spectrometer (PTR-MS). These species are emitted in diesel exhaust and may be important precursors to secondary organic aerosol production in urban areas. Long chain alkanes undergo dissociative proton transfer reactions forming a series of fragment ions with formula CnH2n+1. The yield of the fragment ions is a function of drift conditions. At a drift field strength of 80 Townsends, the most abundant ion fragments from C10 to C16 n-alkanes were m/z 57, 71 and 85. The PTR-MS is insensitive to n-alkanes less than C8 but displays an increasing sensitivity for larger alkanes. Higher drift field strengths yield greater normalized sensitivity implying that the proton affinity of the long chain n-alkanes is less than H2O. Analysis of diesel fuel shows the mass spectrum was dominated by alkanes (CnH2n+1), monocyclic aromatics, and an ion group with formula CnH2n−1 (m/z 97, 111, 125, 139). The PTR-MS was deployed in Sacramento, CA during the Carbonaceous Aerosols and Radiative Effects Study field experiment in June 2010. The ratio of the m/z 97 to 85 ion intensities in ambient air matched that found in diesel fuel. Total diesel exhaust alkane concentrations calculated from the measured abundance of m/z 85 ranged from the method detection limit of ~1 μg m−3 to 100 μg m−3 in several air pollution episodes. The total diesel exhaust alkane concentration determined by this method was on average a factor of 10 greater than the sum of alkylbenzenes associated with spark ignition vehicle exhaust.

Citation: Erickson, M. H., Wallace, H. W., and Jobson, B. T.: Quantification of diesel exhaust gas phase organics by a thermal desorption proton transfer reaction mass spectrometer, Atmos. Chem. Phys. Discuss., 12, 5389-5423, doi:10.5194/acpd-12-5389-2012, 2012.
 
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