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

Abstract

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 D 1) and SV (using the composition-dependent CE of Middlebrook et al.), as well as SMPS and PILS-IC are compared. Agreement is good in all cases, verifying that CE » 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 (»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 (»0.5% chloride/nitrate) or CV (»0.2% chloride/nitrate). Our results support the improved quantification with the CV AMS and characterize its chemical detection properties.

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

“…Although the CE of some pure inorganic species were still less than 1 in the CV, a higher CE (∼ 1) has been observed for ambient internally mixed particles (Hu et al, 2017).…”

“…RIE SO 4 ∼ 1.2 was found in the SV in this study, the same as the default value in the AMS analysis software. RIE SO 4 in the CV in this study was ∼ 1.7-2.4, significantly larger than in the SV, although values as low as 1.1 have been observed in the CV with ACSM (Hu et al, 2017). Sulfate RIE can be influenced by many aspects including detailed ionizer, vapourizer, filament positions and turning of ion optics.…”

“…This effect will be most important for laboratory experiments with monodisperse particles. For ambient air with typically broad size distributions, size distributions measured from an AMS using the CV are expected to be useful (Hu et al, 2017). A method for estimating whether a pure species can be detected by the AMS sizing mode at a given T v is proposed.…”

“…13b1-2). However, size distributions in ambient air tend to be broad, and when the size calibration curve of (NH 4 ) 2 SO 4 is applied, a consistent size distribution measurement between the SV and CV is found, suggesting that the size distribution measurement in the CV is still useful (Hu et al, 2017). Figure 13.…”

Volatility measurement of atmospheric submicron aerosols in an urban atmosphere in southern China

“…A scanning mobility particle sizer (SMPS, TSI, Inc.) was used to measure the particle number size distribution (mobility diameter: 15-600 nm) with a time resolution of 5 min. By assuming the densities of the components obtained in the literature (Kuwata et al, 2012;Poulain et al, 2014;Hu et al, 2017), the corresponding mass concentration can be calculated from the particle number size distribution. The AE-31 and SMPS were used only for ambient sampling.…”