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Condensed Particle Counters
and
Scanning Mobility Particle Sizer

CPC and SMPS

Atmospheric particles appear in variable concentrations and over a size range from a few nm until several 10 um. The number concentration of aerosol particles is measured with a Condensed Particle Counters (CPC). To determine the aerosol particle size distribution, a Scanning Mobility Particle Sizer (SMPS) is applied.

Condensed Particle Counters and Scanning Mobility Particle Sizer

In order to detect submicron particles by optical techniques they must have a certain minimum diameter – determined by the wavelength of the light used for detection. In a CPC the particles are therefore exposed to a high supersaturation of a condensation fluid (water or butanol). The particles grow due to rapid condensation and are then counted with an optical detector. With the available instruments (TSI model 3022a, 3025, 3785, 3786) particles of sizes between 2.5 and 3 µm can be detected in concentrations up to 107 particles/cm3.

The SMPS is the combination of a particle size selector (Differential Mobility Analyzer, DMA) and a CPC. For size selection the DMA uses the fact that a fraction of all aerosol particles is naturally charged and that their movements in an electric field are proportional to their size. By scanning the voltage generating the electric field in the DMA in which the particles drift particle size is selected. Measuring the particle concentration for each selected size with a CPC then gives the particle size distribution. The standard SMPS (TSI model 3081) covers the size range from 10 to 1000 nm. With the Nano DMA (TSI model 3085) particles between 2 and 150 nm can be detected.


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