Instrument - High-resolution time-of-flight aerosol mass spectrometer
High-resolution time-of-flight aerosol mass spectrometer
What is being measured:
Submicrometer, nonrefractory aerosol chemical composition; chemical speciation of sulfate, nitrate, ammonium, chloride, and organic aerosol constituents.
Data recording software:
ToF-AMS DAQ v4.0.40
Data analysis software:
SQUIRREL v1.61 and PIKA v1.21 modules for Igor Pro
Raw data time resolution:
Analysis data averaging:
Detection limits for each class of chemical constituents are calculated as three times the standard deviation of blank signals measured from HEPA filter samples taken before each experiment.
Sensitivity to temperature (and correction method, if applicable):
Sensitivity to relative humidity (and correction method, if applicable):
Sample preparation method:
Submicrometer aerosol (35 nm-1.5 um) is sampled into the instrument through an aerodynamic lens at a flow rate of ~1.3 mL/s, producing a collimated particle beam that is directed onto a resistively heated surface where particles undergo vaporization (~600
Sample residence time (chamber to instrument) (seconds):
Length of tubing (cm):
Instrument flow rate:
Tubing inner diameter:
Chemical identification method:
Ions formed via electron impact ionization are detected with a custom-designed Tofwerk HR-ToF-MS configured in V-mode and operating at a mass resolution of ~2100.
Data analysis method:
Data are analyzed using the SQUIRREL v1.61 and PIKA v1.21 modules for Igor Pro, and are corrected for gas-phase interferences and composition-dependent collection efficiencies.
he instrumental ionization efficiency is calibrated using dry, 350 nm ammonium nitrate particles. Mass loadings of sulfate, ammonium, chloride, and organic aerosol constituents are reported as "nitrate equivalent mass loadings (ug/m3)," assuming ionization efficiencies for these species relative to nitrate.
The instrumental ionization efficiency is calibrated using dry, 350 nm ammonium nitrate particles, generated via atomization of a dilute (0.01 M) aqueous solution of ammonium nitrate and size-selected with a DMA
Calibration drift estimate:
Low (on the order of weeks)
Uncertainty estimation method:
Mass spectral "air peaks," e.g., N2 interfering with aerosol-derived CO at m/z 28, are the most common interferences.
Link to supplemental information:
The working principles, modes of operation, and analysis protocols for the HR-ToF-AMS have been extensively documented in the literature, so only brief descriptions are provided here.
(a) O:C (+/- 30%), (b) H:C (+/- 10%)