A versatile flat-deposit impactor-type aerosol collector - Part 1: Design and qualitative study

Cascade impactors provide an efficient method for sampling aerosols accordi ng to their size, grossly between 0.1 mu m and a few tens of microns in dia meter. We have designed such an apparatus, with rotatable substrate plates and radially aligned rectangular orifices. The nominal cutpoint diameters a re, respectively, 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 s et of orifice plates for operation at 20 L/min giving the same cutpoint cha racteristics. Annular deposits are obtained following complete rotation of the collecting substrates. The airflow is controlled with a critical orific e at the last stage. A calculation program was written for a rectangular or ifice 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 condi tions of ambient temperature and pressure. The SPAL sampler has proven sati sfactory with respect to manipulations required, maintenance, and results d elivered.