AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
A Novel Compact Aerosol Mass Spectrometer - the ToF-ACSM: Instrument Performance and First Field Deployment
Roman Fröhlich, MICHAEL CUBISON, Jay Slowik, Andre Prévôt, Urs Baltensperger, Urs Rohner, Marc Gonin, Joel Kimmel, Douglas Worsnop, John Jayne, Tofwerk AG
Abstract Number: 291 Working Group: Instrumentation and Methods
Abstract The Aerodyne Aerosol Mass Spectrometer (AMS) (Jayne, 2000) provides quantitative, highly time-resolved mass spectra of non-refractory, submicron particles. These data have been widely used to quantify inorganic species and organic material, segregate primary and secondary aerosol, and identify certain primary sources. The Aerosol Chemical Speciation Monitor (ACSM) (Ng, 2011) is a low-cost version of the AMS designed for long-term operation and stability. Its small size also makes it well-suited for integration into existing monitoring stations, or other locations where space is limited. However, the quadrupole-based ACSM (hereafter denoted ``Q-ACSM'') is much less sensitive than the standard AMS, constraining both detection limits and achievable temporal resolution. Here we present the testing and initial deployment of a new Time-of-Flight ACSM (ToF-ACSM).
The new Tofwerk E-ToF mass spectrometer employed in the ToF-ACSM yields a higher mass spectrometer duty cycle and improved sensitivity with respect to the Quad. Preliminary results indicate a hardware dependent improvement of the detection limits compared to the Q-ACSM of a factor of 4-18 (organics). This means that the detection limits lie between that of the W- and V-mode HR-ToF-AMS. With a resolving power of 300-500 mTh/Th, isobaric mass peaks are easily resolved, and even the mass excess of ions is discernible.
We will report instrument performance, including detection limits, short- and long-term stability and maintenance requirements. An intercomparison of the ToF-ACSM with Q-ACSM and a high resolution (HR-) ToF-AMS will be presented. Furthermore we will present first ToF-ACSM field data from deployment at the high-altitude Jungfraujoch station, which resides in the free troposphere for most of the year (Baltensperger, 1997). The low aerosol concentrations at this site provide an ideal test case for the ACSM. Finally we will demonstrate the application of the positive matrix factorization (PMF) (Ulbrich, 2009) source appointment method to the ToF-ACSM data.