Abstract View
Nonrefractory Particulate Matter Detection Using the Dual-Vaporizer Configuration of the Soot Particle Aerosol Mass Spectrometer (SP-AMS)
LEAH WILLIAMS, Anita Avery, Arthur J. Sedlacek, Timothy Onasch, Aerodyne Research, Inc.
Abstract Number: 498
Working Group: Aerosol Chemistry
Abstract
The 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 black carbon (rBC) and metal nanoparticles, and associated NR-PM. The SP-AMS can also be operated with both vaporizers by sequentially turning the laser vaporizer on and off. The use of both vaporizers simultaneously is complicated by different collection efficiencies (CE) and different relative ionization efficiencies (RIE) of NR-PM species that can strongly affect the measured NR-PM signals from rBC-containing particles. This work describes a systematic investigation of mixed particles with varying ratios of ammonium nitrate, ammonium sulfate or levoglucosan to rBC. Particles were generated by atomizing aqueous solutions with specific mass ratios of NR-PM material to rBC and size-selecting with a differential mobility analyzer (DMA). The composition of the particles was confirmed with a Single Particle Soot Photometer (SP2) to be the expected mixture of NR-PM and rBC and to be an internal mixture. Particle bounce at the tungsten vaporizer was assessed with a quadrupole (Q-) AMS equipped with a light scattering module. NR-PM and rBC mass concentrations were measured with an SP-AMS in both laser on and laser off modes. This dataset shows that CE at the tungsten vaporizer varies strongly with composition due to increasing bounce for particles with a higher fraction of rBC for the particle sizes used here (300 to 400 nm). 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, in addition to different RIEs, causes an apparent increase in NR-PM signal when the laser is on.