AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Evaluation of the New Capture Vaporizer for Aerosol Mass Spectrometers (AMS): Fragmentation, Elemental Ratio and Source Apportionment, Quantification of Organic Aerosols (OA)
WEIWEI HU, Douglas Day, Pedro Campuzano-Jost, Benjamin A. Nault, Taehyun Park, Taehyoung Lee, Philip Croteau, Manjula Canagaratna, John Jayne, Douglas Worsnop, Jose-Luis Jimenez, CIRES, University of Colorado, Boulder
Abstract Number: 232 Working Group: Instrumentation and Methods
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 commercial instruments, a collection efficiency (CE) correction, varying with aerosol phase and chemical composition (Middlebrook et al., 2012) is needed to account for the particle bounce loss in the SV. Recently, a new “capture vaporizer” (CV) has been designed and successfully used to achieve CE~1 for ambient aerosols (Hu et al., 2017;Xu et al., 2017). Recent publications characterize the quantification of the inorganic species and total aerosol mass. This study reports on the performance of organic aerosol (OA) in CV-AMS regarding fragmentation, elemental ratios and source apportionment of OA for the first time. The quantification of OA in the CV including how oxidation and morphology affects CE and RIE of OA is also discussed. Compared with the spectra from the SV, the larger molecular-weight fragments of OA tend to shift toward smaller ions in the CV due to additional thermal decomposition arising from increased residence time and hot surface collisions. Unexpected CO+ ions (and to a lesser extent, H2O+) when sampling long chain alkane/alkene-like OA (e.g. squalene) in the CV are probably caused by chemical interactions between sampled OA and residues on the vaporizer surfaces. No evidence for such CO+ enhancement is found when studying the ambient OA. The elemental composition of pure OA standards and ambient OA can be accurately measured with the CV, with suitable modifications to the quantification procedure. Consistent variation of PMF factors and their fractions in total OA were found between the ambient CV and SV datasets no matter if biogenic- or anthropogenic- emissions dominate OA production, indicating no or limited loss of information despite the increased fragmentation.