Tropospheric Chemistry: Instruments

Compact Time-of-Flight Aerosol Mass Spectrometer (C-ToF AMS) with Light Scattering

AMS instrument — C-ToF AMS on the NOAA Twin Otter for the 2017 UWFPS field campaign.

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.

Modifications

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 C-ToF AMS a one-of-a-kind instrument for field and laboratory aerosol chemical composition measurements.

Species Measured

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.

Manufacturer

Originally built by Aerodyne Research Inc. in 2002 and modified with custom components plus upgraded and optional hardware.

Major Field Projects / Platforms

2002 NEAQS (NOAA R/V Ronald H. Brown)
2006 TexAQS/GoMACCS (NOAA WP-3D)
2008 ARCPAC (NOAA WP-3D)
2009 ACCRONIM (NOAA Boulder Kohler Mesa)
2010 CalNex (NOAA WP-3D)
2010 Gulf Deepwater Horizon Oil Spill (NOAA WP-3D)
2011 NACHTT (NOAA Boulder Atmospheric Observatory tower)
2013 SENEX (NOAA WP-3D)
2016 FIREX FireLab (USFS Fire Sciences Lab)
2017 UWFPS (NOAA Twin Otter)

Key Publications

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.