Evaluation of the new capture vaporizer for aerosol mass spectrometers (AMS) through field studies of inorganic species

The aerosol mass spectrometer (AMS) and aerosol chemical speciation monitor (ACSM) are widely used for quantifying aerosol composition. The quantification uncertainty of these instruments is dominated by the collection efficiency (CE) due to particle bounce. A new capture vaporizer (CV) has been recently developed to achieve unit CE. In this study, we examine the performance of the CV while sampling ambient aerosols. AMS/ACSMs using the original standard vaporizer (SV) and CV were operated in parallel during three field studies. Concentrations measured with the CV (assuming CE = 1) and SV (using the composition-dependent CE of Middlebrook etal.), as well as SMPS and PILS-IC are compared. Agreement is good in all cases, verifying that CE approximate to 1 in the CV when sampling ambient particles. Specific findings include: (a) The fragmentation pattern of ambient nitrate and sulfate species observed with the CV was shifted to smaller m/z, suggesting additional thermal decomposition. (b) The differences in fragmentation patterns of organic vs. inorganic nitrate and sulfur species are still distinguishable in the CV, however, with much lower signal-to-noise compared to the SV. (c) Size distribution broadening is significant, but its impact is limited in field studies since ambient distributions are typically quite broad. Consistent size distributions were measured with the SV and CV. (d) In biogenic areas, UMR nitrate is overestimated based on the default fragmentation table (approximate to factor of 2-3 in SOAS) for both vaporizers, due to underestimation of the organic interferences. We also report a new type of small interference: artifact chloride signal can be observed in the AMS when high nitrate mass concentration is sampled with both the SV (approximate to 0.5% chloride/nitrate) or CV (approximate to 0.2% chloride/nitrate). Our results support the improved quantification with the CV AMS and characterize its chemical detection properties.Copyright (c) 2017 American Association for Aerosol Research