AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Evaluation of a Particle Trap Laser Desorption Mass Spectrometer (PT-LDMS) for Online Measurements of Aerosol Composition
NOBUYUKI TAKEGAWA, Takuma Miyakawa, Naoki Takeda, Masahiko Takei, Noritomo Hirayama, RCAST, University of Tokyo
Abstract Number: 292 Working Group: Instrumentation and Methods
Abstract We have developed a new aerosol composition analyzer, a particle trap laser desorption mass spectrometer (PT-LDMS), for online measurements of sulfate, nitrate, and organic carbon (OC). The main components of the instrument include an aerodynamic lens, a particle trap (micro-machined mesh layers coated by platinum), a quartz cell, an electron impact ionization quadrupole mass spectrometer (QMS), and a carbon dioxide (CO2) laser. Aerosol particles collected on the particle trap are vaporized by the CO2 laser and the ion signals from the evolved gas are detected by the QMS. The quantification of sulfate and nitrate is performed by detecting major fragments of these compounds. The quantification of OC is performed by catalytically converting organic compounds to relatively simple, low-molecular-weight compounds on the heated surface of the particle trap. The cycle time of the particle collection and laser desorption is typically 10 min. The concept of the PT-LDMS and first evaluation of its performance in the laboratory was given by Takegawa et al. (Aerosol Sci. Tech., 2012). Here we present further improvements and evaluation of the instrument. The fragment patterns of ammonium sulfate, ammonium nitrate, and some selected organic compounds (oxalic acid, oleic acid, glucose, etc.) were tested in the laboratory. The mass-to-charge ratios (m/z) of 48 (SO) + 64 (SO2) and 30 (NO) were the major fragments of sulfate and nitrate, respectively, and the yields of these signals per unit mass loading were reproducible. The fragments of the selected organic compounds were predominantly found at lower m/z (< 50), mostly at m/z 44 (CO2). The optimizations of the laser desorption process and the structure of the trap are now being performed to achieve high conversion efficiency for various organic compounds. Preliminary results from the ambient measurements and intercomparison with other instruments will also be discussed in the presentation.