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It is shown that a simple optical particle-counting system can be efficiently and accurately used for determining the mass of collected particles during the calibration of a cascade impactor. For particles larger than 1 mu m in diameter, the limit of detection was enhanced by a factor 5 compared to the traditional spectrophotometer-based method.

Cascade impactors provide an efficient method for sampling aerosols according to their size, grossly between 0.1 mu m and a few tens of microns in diameter. We have designed such an apparatus, with rotatable substrate plates and radially aligned rectangular orifices. The nominal cutpoint diameters are, respec tively, for stages 1-7 of the collector: 10, 5, 2, 1, 0.5, 0.25, and 0.1 mu m aed for an airflow of 10/L min. The sampler has an auxiliary set of orifice plates for operation at 20/L min giving the same cutpoint characteristics. Annular deposits are obtained following complete rotation of the collecting substrates. The airflow is controlled with a critical orifice at the last stage. A calculation program was written for a rectangular orifice impactor in order to determine the cutpoints in different conditions. The constant exit pressure mode of operation appears to be the best way to minimize fluctuations of the effective cutpoints against the varying conditions of ambient temperature and pressure. T...

The SPAL collector is a versatile impactor-type aerosol collector with rotatable substrate plates and radially aligned slot orifices. The airflow, controlled with a critical orifice at the last stage, becomes choked for an exit pressure of 0.5 atm or less. Monodisperse latex and methylene blue aerosols sampled on coated and uncoated aluminum foil substrates were used to determine the particle cutpoint diameters of each stage (9.0-0.07 mu m aed), loss on walls (3-7% for 0.054 mu m particles), and overall efficiency (97% from 0.3 to 7 mu m). Quantitative measurements were made with a spectrophotometer after recovering aerosols with a water and surfactant solution and with a semiautomated particle counting system using phase contrast microscopy. The experimental cutpoints and mea sured interstage pressures compare well with theory.