Comparison of an optical particle size monitor and a cascade impactor for in-stack source testing

Particle size measurements by a prototype in-stack optical particle size monitor are compared to concurrent particle size measurements by an in-stack cascade impactor at three coal-fired fly ash sources. The results indicate that the optical monitor and impactor size measurements defined similar particle size distributions between 0.2 and 20 mu m. Particles smaller than 0.2 mu m, as expected, were not observed by the optical sizer. Particles larger than 20 mu m were also expected to be detectable, but the optical instruments may have some sensitivity to the larger size particles. Mean size measurements by the optical instrument were always larger than median size measurements by the impactor. The difference was 16 and 36% for two tests conditions where the fine particle fractions below 0.2 mu m were small. The difference increased to 57 and 151% for two test conditions where the fine particle fractions below 0.2 mu m were large.