Particle detection using the dual-vaporizer configuration of the soot particle Aerosol Mass Spectrometer (SP-AMS)

Abstract

The Aerodyne Soot Particle Aerosol Mass Spectrometer (SP-AMS) can operate with one or both of two particle vaporizers: (1) the standard resistively heated tungsten vaporizer (TV) for detection of non-refractory particulate matter (NR-PM), and (2) an intracavity laser vaporizer (LV) for detection of absorbing, refractory materials, including refractory black carbon (rBC), metal nanoparticles, and associated coatings. In addition to using these vaporizers individually, both can be used simultaneously (dual vaporizer, DV, mode), commonly implemented by sequentially turning the laser vaporizer on (DV-Lon) and off (DV-Loff). Recent results in DV mode have shown an apparent enhancement in measured NR-PM signal during DV-Lon compared with DV-Loff, even for inorganic species unlikely to be strongly associated with rBC. The use of dual vaporizers is complicated by different collection efficiencies (CE) of the two vaporizers, potential differences in the relative ionization efficiencies (RIE) for the same species vaporized from the two vaporizers, and potential interference between the two vaporizers due to laser heating of AMS internal components. Here, we investigated the effect of the laser-heating interference on NR-PM signal. We tested a variety of laser baffles to minimize laser-heating interferences and to constrain the alignment of the laser vaporizer and we identified a baffle that meets these criteria and can be incorporated into SP-AMS systems. For well aligned standard and laser vaporizers, laser heating was found to have only a minor effect on the NR-PM ion signals. Most of the observed increases in NR-PM signals during DV-Lon are attributed to vaporizer-specific differences in the CE and RIE values of NR-PM associated with the rBC-containing particles. Copyright © 2020 American Association for Aerosol Research.