Aerodynamic particle sizer, measurement

For a spherical particle of nonunit density the classical aerodynamic diameter is different from its physical diameter and it depends on its density. Aerosol instruments like the cascade impactor and aerodynamic particle sizer measure the classical aerodynamic diameter of atmospheric particles, which is in general different from the physical diameter of the particles even if they are spherical. 

APS (aerodynamic particle sizer)—measures the aerodynamic particle diameter. Da, by monitoring the settling velocity of namomaterials. Results are referenced to a spherical particle with a density of 1 g/cm. ... 

A related technique that is suitable for measurement of aerosols at lower mass loadings is the aerodynamic particle sizer (3, 10). In this instrument the aerosol is rapidly accelerated through a small nozzle. Because of their inertia, particles of different aerodynamic sizes are accelerated to different velocities, and the smallest particles reach the highest speeds. The particle velocity is measured at the outlet of the nozzle. From the measurements of velocities of individual particles, particle size distributions can be determined. The instrument provides excellent size resolution for particles larger than about 0.8 xm in diameter, although sampling difficulties limit its usefulness above 10 xm. 

Naqui et. al. [153] describe a phase Doppler technique, for measuring particle velocity and statistcal information about particle size of irregular particles, based on a phase shift signal. The technique works on near back-scatter which leads to a robust set-up under conditions of limited optical access. Preliminary measurements in a crystallizer were presented and good agreement with TSI Aerodynamic particle sizer was found. 

Instruments using the residence time, such as the aerodynamic particle sizers, or the particle velocity, as used by the phase Doppler particle analyzers, measure the particle size primarily based on the aerodynamic diameter. 

For larger particles or nanoparticle aggregates, SMPS measurements can be coupled with an aerodynamic particle sizer (APS). For spherical particles, it is easy to relate the measured diameters from the SMPS and APS because no corrections need to be made for shape and volume, but for irregularly shaped particles the APS reports an aerodynamic diameter. Da, by comparing the settling velocity to a spherical particle with a density of 1 g cm to compute the particle size. A volume equivalent diameter, D g, which is defined as the volume of a sphere with the same volume as a particle with an irregular shape, is used to relate the aerodynamic diameter from the APS with mobility diameter, D , from the SMPS (46) ... 

The condensation particle counter battery measurements are complemented by aerosol particle size distribution measurements using a dual differential mobility particle sizer system covering a size range of 3-900 nm, and an aerodynamic particle sizer covering aerosol particle sizes between 0.7 and 20 pm. In addition, air ions are detected using a balanced scanning mobility analyser and an air ion spectrometer. During the period of measurements, several new particle formation (nucleation) events occur in tropospheric air. 

Figure 6.22. The TSI Aerodynamic Particle Sizer Model 3320 measures the velocity of fineparticles passing through a so-called double crested laser beam in order to determine their size from the acceleration they experience at the nozzle. (Larger fineparticles accelerate more slowly and so have a lower velocity.) a) Layout of the TSI Aerodynamic Particle Sizer, b) View of the inspection zone from above, c) Enlarged side view looking into the laser beam.

Fig. 7 A Doppler-shift procedure for measuring the aerodynamic size of aerosol fine particles is used by the TSI aerosol particle sizer. (From...

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