Detection of Refractory and Nonrefractory Aerosol Mixtures Using the Dual-Vaporizer Configuration of the Soot Particle Aerosol Mass Spectrometer (SP-AMS)
ANITA AVERY, Leah Williams, Edward Fortner, Timothy Onasch,
Aerodyne Research, Inc. Abstract Number: 431
Working Group: Instrumentation and Methods
AbstractThe Soot Particle-Aerosol Mass Spectrometer (SP-AMS) can operate with one of two particle vaporizers: (1) the standard AMS resistively heated tungsten vaporizer for traditional detection of non-refractory particulate matter (NR-PM), and (2) an intracavity laser vaporizer for detection of absorbing, refractory materials, including refractory black carbon (rBC). Measurements of both refractory and non-refractory compounds can be achieved by sequentially turning the laser vaporizer on and off over the course of sampling. The nonrefractory component of internally mixed aerosols is detected in both laser states, but with different collection efficiencies (CE) and different relative ionization efficiencies (RIE). This work describes a systematic investigation of particles of ammonium nitrate, ammonium sulfate or levoglucosan associated with rBC (Cab-o-Jet) generated by atomizing aqueous solutions. Ratios of refractory:NR content by solution mass varied from 1:9 to 9:1, and the resulting aerosol were size selected to 300nm with a DMA. The presence of internally mixed particles was confirmed with a Single Particle Soot Photometer (SP2). Particle bounce at the tungsten vaporizer was assessed with a quadrupole (Q-) AMS equipped with a light scattering module. The SP-AMS switched between laser on and laser off modes, and also collected particle time of flight (PToF) and beam width probe (BWP) measurements to analyze aerosol compactness. As expected, the CE for the tungsten varies strongly with rBC fraction due to increasing bounce for particles with more rBC. CE at the laser vaporizer also decreases with increasing rBC due to particle beam focusing, but not as strongly. The interplay of these two CEs causes an apparent increase in NR-PM signal when the laser is on.