10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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An Overview on Evaluation of the New Capture Vaporizer for Aerosol Mass Spectrometers (AMS)
WEIWEI HU, Pedro Campuzano-Jost, Douglas Day, Benjamin A. Nault, Taehyun Park, Taehyoung Lee, Aki Pajunoja, Annele Virtanen, Philip Croteau, Manjula Canagaratna, John Jayne, Douglas Worsnop, Jose-Luis Jimenez, CIRES, University of Colorado, Boulder
Abstract Number: 919 Working Group: Instrumentation
Abstract The Aerosol Mass Spectrometer (AMS) and Aerosol Chemical Speciation Monitor (ACSM) are widely used for quantifying submicron aerosol mass concentration and composition. Using the standard vaporizer (SV) installed in almost all currently-operating instruments, a collection efficiency (CE) correction, varying with aerosol phase and chemical composition, is needed to account for particle bounce losses, which dominate the uncertainty on quantification of concentrations. To address this limitation, a new capture vaporizer (CV) was recently built and tested in various laboratory and field measurements. Here, we present an overview of results on CV quantification and spectrum characterization for laboratory-generated compounds and ambient aerosols, with comparisons results from co-sampled SV-AMS and other independent measurement. We found CV-AMS has an improved CE for less volatile compounds (e.g., pure (NH4)2SO4 in the lab) and achieves CE~1 for ambient aerosols. However, the CV chemical detection properties show some differences from the SV due to the increased residence time of particles and vaporized molecules inside the CV, and different vaporizer materials. The effects of oxidation and heating of aerosols on quantification using both vaporizers is also examined. Artifact CO+ ions (and to a lesser extent, H2O+), when sampling long chain reduced OA (e.g. squalene) in the CV, are observed, probably caused by chemical reactions between sampled OA and molybdenum oxides on the vaporizer surfaces (with the carbon derived from the incident OA). No evidence for such CO+ enhancement is observed for highly oxidized species and ambient OA. The elemental composition and source apportionment (PMF) with the CV can be accurately determined after proper calibration. The size distribution broadening is significant for monodisperse particles, but its impact is limited in field studies since ambient distributions are typically quite broad. Consistent size distributions of ambient aerosols were measured with the SV and CV after calibration. Finally, we summarize all the relevant pros and cons when using the CV versus SV.