Demonstration of a VUV lamp photoionization source for improvedorganic speciation in an aerosol mass spectrometer
In recent years, the Aerodyne AerosolMass Spectrometer(AMS) has become a widely used tool for determining aerosol sizedistributions and chemical composition for non-refractory inorganic andorganic aerosol. The current version of the AMS uses a combination offlash thermal vaporization and 70 eV electron impact (EI) ionization.However, EI causes extensive fragmentation and mass spectra of organicaerosols are difficult to deconvolute because they are composites of theoverlapping fragmentation patterns of all species present. Previous AMSstudies have been limited to classifying organics in broad categoriessuch as oxidized and hydrocarbon-like." In this manuscript we present newefforts to gain more information about organic aerosol composition byemploying the softer technique of vacuum ultraviolet (VUV) ionization ina Time-of-Flight AMS (ToF-AMS). In our novel design a VUV lamp is placedin direct proximity of the ionization region of the AMS, with only awindow separating the lamp and the ionizer. This design allows foralternation of photoionization and electron impact ionization within thesame instrument on the timescale of minutes. Thus, the EI-basedquantification capability of the AMS is retained while improved spectralinterpretation is made possible by combined analysis of the complementaryVUV and EI ionization spectra. Photoionization and electron impactionization spectra are compared for a number of compounds including oleicacid, long chain hydrocarbons, and cigarette smoke. In general, the VUVspectra contain much less fragmentation than the EI spectra and for manycompounds the parent ion is the dominant ion in the VUV spectrum. As anexample of the usefulness of the integration of PI within the fullcapability of the ToF-AMS, size distributions and size-segregated massspectra are examined for the cigarette smoke analysis. As a finalevaluation of the new VUV module, spectra for oleic acid are compared tosimilar experiments conducted using the tunable VUV radiation(synchrotron) at the Advanced Light Source in Berkeley, CA. Futuretechnical modifications for improvements to the sensitivity of thetechnique and its potential for ambient measurements will bediscussed.
- Research Organization:
- COLLABORATION - Aerodyne Research,Inc./MA
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 919395
- Report Number(s):
- LBNL-62873; ASTYDQ; R&D Project: 403101; BnR: KC0301020; TRN: US0806370
- Journal Information:
- Aerosol Science and Technology, Vol. 41, Issue 9; Related Information: Journal Publication Date: September2007; ISSN 0278-6826
- Country of Publication:
- United States
- Language:
- English
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