Short name:
SEMS

Full name:
Scanning electrical mobility system

What is being measured:
Particle size distribution

Sampling Protocol:
Online

Manufacturer:
Brechtel

Model:
Model 2002

Instrument year :
2013

Data recording software:

Data analysis software:
Igor Pro v6

Raw data time resolution:
1 minute

Analysis data averaging:

Detection limit:
To be filled

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

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

Sampling method:
Direct sampling

Sample preparation method:
None

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

Length of tubing (cm):

Instrument flow rate:
0.35 lpm

Tubing inner diameter:
1/4 inch

Tubing material:
Copper

Chemical identification method:
The SEMS consists of a differential mobility analyzer (DMA) and a butanol-based condensation particle counter (CPC, model 1710, Brechtel). An air sample is drawn through a pre-impactor inlet, which removes particles larger than 2 μm, and is then dried using a concentric nafion dryer with 1.6 lpm dry air sheath flow. The polydisperse sample then passes through a Po210 charge neutralizer (model 9000, Brechtel) to ensure a Boltzmann charge distribution. Once the sample enters the DMA column, particle size-selection is achieved by varying the electric field strength. The electrical mobility (i.e. the ability to transverse an electric field) of a charged particle is a function of its size. Because the physical dimensions of the DMA column (e.g. distance between the entrance and the exit) are fixed, only monodisperse particles of the desired size can pass through the DMA column at any given field strength.

Data analysis method:

Quantification method:
The monodisperse flow then passes through a wet wick containing n-butanol, which can condense onto the sample particles, leading to uniform size growth. The number of particles is counted by the CPC via light scattering. The counting efficiency decreases with decreasing particles size (hence the necessity for particle growth), which is accounted for by the SEMS data acquisition software. By stepping through different DMA voltage ranges, particles of different size ranges can be counted, and a particle size distribution can be obtained. Although the SEMS can detect particles up to 2 μm, it is configured to characterize particles ranging between 12 to 1000 nm in diameter. The sample flow rate and the DMA column sheath flow rates are 0.35 and 5 slpm, respectively. Knowing the particle size and number count, the particle surface area and volume distributions can be calculated. Knowledge of the particle density is required for volume to mass conversion.

Calibration method:
Done in parallel with ACSM calibration. Refer to that calibration procedure.

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: