Principle of the Measurement
Ambient aerosols are sampled into a vacuum chamber, focused with an aerodynamic lens into a beam, impacted on a vaporizer, and evaporated into the electron impact ionization source of a mass spectrometer. Mass distributions are measured using a particle-beam chopper at the exit of the lens and the particle time-of-flight in the vacuum chamber between the chopper and the time the signals are detected in the mass spectrometer.
A major upgrade in 2007 was swapping the original quadrupole mass spectrometer for a compact time-of-flight mass spectrometer. Customizations are continuously being made to operate the instrument semi-autonomously or aboard NOAA aircraft (special rack, pressure-controlled sampling inlet, rewiring power sources, pneumatically controlled inlet valve, etc.). The optional light scattering module was added in 2012 to determine the in-situ collection efficiency. This combination of customizations, upgrades, and options makes CSL's LS-C-ToF AMS a one-of-a-kind instrument for field and laboratory aerosol chemical composition measurements.
Non-refractory submicron aerosol composition, including aerosol sulfate, nitrate, ammonium, chloride, and organic material.
Airborne Detection Limits and Time Response*
Sulfate: ~0.03 µg sm-3 in 10 seconds
Nitrate: ~0.04 µg sm-3 in 10 seconds
Ammonium: ~0.09 µg sm-3 in 10 seconds
Chloride: ~0.07 µg sm-3 in 10 seconds
Organic mass: ~0.3 µg sm-3 in 10 seconds
*Detection limits are from the 2017 UWFPS field campaign aboard the NOAA Twin Otter, using averages from 2-9 hours after starting the pumps.
Originally built by Aerodyne Research Inc. in 2002 and modified with custom components plus upgraded and optional hardware.
Major Field Projects / Platforms
Liao, J., C.A. Brock, D.M. Murphy, D.T. Sueper, A. Welti, and A.M. Middlebrook, Single particle measurements of bouncing particles and in-situ collection efficiency of an airborne aerosol mass spectrometer (AMS) with light scattering detection, Atmospheric Measurement Techniques, doi:10.5194/amt-10-3801-2017, 2017.
Middlebrook, A. M., R. Bahreini, J. L. Jimenez, and M. R. Canagaratna, Evaluation of composition-dependent collection efficiencies for the Aerodyne aerosol mass spectrometer using field data, Aerosol Sci. Technol., doi:10.1080/02786826.2011.620041, 2012.
Bahreini, R., B. Ervens, A. M. Middlebrook, C. Warneke, J. A. de Gouw, P. F. DeCarlo, J. L. Jimenez, C. A. Brock, J. A. Neuman, T. B. Ryerson, H. Stark, E. Atlas, J. Brioude, A. Fried, J. S. Holloway, J. Peischl, D. Richter, J. Walega, P. Weibring, A. G. Wollny, and F. C. Fehsenfeld, Organic aerosol formation in urban and industrial plumes near Houston and Dallas, Texas, J. Geophys. Res., doi:10.1029/2008JD011493, 2009.
Matthew, B. M., A. M. Middlebrook, and T. B. Onasch, Collection efficiencies in an Aerodyne aerosol mass spectrometer as a function of particle phase for laboratory generated aerosols, Aerosol Sci. Technol., doi:10.1080/02786820802356797, 2008.
Bahreini, R., E. J. Dunlea, B. M. Matthew, C. Simons, K. S. Docherty, P. F. DeCarlo, J. L. Jimenez, C. A. Brock, and A. M. Middlebrook, Design and operation of a pressure-controlled inlet for airborne sampling with an aerodynamic aerosol lens, Aerosol Sci. Technol., doi:10.1080/02786820802178514, 2008.