Performance analysis of the cascade impactor, the federal reference method PM 2.5 sampler, and the improve PM 2.5 sampler

Abstract

The concept of jet impaction has been a common method used in ambient air quality and personal particulate matter(PM) monitors, as a means of removing PM out of an air stream, for the purpose of monitoring PM concentrations. Two such devices are the cascade impactor and the new Federal Reference Method(FRM) PM₂₅̣ sampler. The FRM PM₂₅̣ sampler was mandated in July 1997, with the passing of new National Ambient Air Quality Standard(NAAQS) for PM. The cascade impactor is the Environmental Protection Agency's(EPA) reference method of determining a particle size distribution(PSD): a distribution of particle mass versus aerodynamic equivalent diameter(AED). This sampler uses jet impaction, to separate PM into fractions of known sizes. There have been documented problems with the cascade impactor and suspicions over its accuracy. In this thesis research, the collected PM fractions from the cascade impactor will be subjected to analysis by the Coulter Counter Multisizer to verify inaccuracies. The new FRM sampler also uses jet impaction. The accuracy of this sampler too, is cause for concern; not only does it use the same principles as the cascade impactor but it was mandated as a PM₂₅̣ sampler "by design'' rather than by performance, implying that it is not known if in fact, the sampler is accurate by performance. Extensive research in the design and performance of cyclones has been done at the Agricultural Engineering Department of Texas A&M University. The results of this research suggest that the efficiency of PM removal is increased with the number of 360 ̊turns that the inlet air stream makes. The FRM sampler uses only four 90 ̊turns at the impaction surface. The hypothesis was then formulated that the new FRM sampler was in fact, inaccurate.