Instrument - Aerosol Chemical Speciation Monitor

Short name:

Full name:
Aerosol Chemical Speciation Monitor

What is being measured:
Bulk aerosol species

Sampling Protocol:



Instrument year :

Data recording software:

Data analysis software:
Igor Pro v6

Raw data time resolution:
1 minute

Analysis data averaging:

Detection limit:
Species dependent

Sensitivity to temperature (and correction method, if applicable): :

Sensitivity to relative humidity (and correction method, if applicable): :

Sampling method:
Direct sampling

Sample preparation method:

Sample residence time (chamber to instrument) (seconds):

Length of tubing (cm):

Instrument flow rate:
0.65 lpm

Tubing inner diameter:
1/4 inch

Tubing material:

Chemical identification method:
Samples are drawn in through an aerodynamic lens, which focuses the sample into a particle beam directed at a 600 C tungsten vaporizer. Non-refractory species (operationally defined) flash-vaporize as they strike the vaporizer, releasing vapors that then undergo electron impact ionization (EI), which is a harsh ionization method that produces positively charged ion fragments. The ions are analyzed by a quadruple residual gas analyzer, yielding unit-mass-resolution data. A standard ion fragmentation table developed for quadruple aerosol mass spectrometers (Q-AMS), which uses the same vaporizer and ionizer, is used to allocate the ion fragments into different species: Organics, sulfate, nitrate, ammonium, or chloride.

Data analysis method:

Quantification method:
The ACSM is equipped with an automatic valve that switches between a filtered and an unfiltered position. In the filtered, or “closed” position, air flow passes through an inline filter which removes most of the particle-phase sample. In the unfiltered, or “open” position, the air flow bypasses the inline filter. During normal data acquisition, hereafter referred to as the “single scan mode,” the ACSM alternates between sampling from the “open” and “closed” position. At either position, air is continuously drawn in through the inlet. Ions between m/z 10 and 150 are detected by the quadruple mass spectrometer at 200 ms amu-1. A full spectrum scan takes roughly 30 seconds. The background-corrected aerosol concentration can be calculated from the differences of “open” and “closed” ion intensity measurements.

Calibration method:
Calibration is performed by first sampling size-selected, 300 nm ammonium nitrate particles using the ACSM and an independent referenced instrument (i.e. CPC). The particles are generated from a dilute solution (0.005 M in water). Size-selection is achieved using the DMA. Ammonium nitrate is chosen because 300 nm ammonium nitrate particles have a CE of 1, meaning that the ACSM and CPC measurement must agree exactly. Knowing the particle density, the expected particle mass can be calculated based on the CPC counts for the monodisperse sample. The nitrate response factor (RFNO3) can then be calculated. The ACSM response to nitrate (NO3) is used as the reference for other species. For any other species, i, the relative ionization efficiency (RIEi) is required for mass conversion.

Calibration drift estimate:
Low (on the order of weeks)

Calibration schedule:
As Needed

Uncertainty estimation method:
To be filled

Known interferences:

Link to supplemental information:

Additional notes:

Measurement uncertainty:

Measurement units: