Performance characteristics of PM₂₅̣ samplers in the presence of agricultural dusts

Abstract

The EPA revised the National Ambient Air Quality Standard (NAAQS) in 1997 to include a standard for fine particulates (PM₂₅̣), and was unanimously upheld by the US Supreme Court in February of 2001. The long-term standard was set at 15 mg/scm, and the short-term standard was set at 65 mg/scm. A PM₂₅̣ sampler was developed for the Federal Reference Method shortly after the revision of the NAAQS, and was mandated "by design" rather than "by performance," due to the limited available performance data. Methods for determining PM₂₅̣ concentrations in the ambient air are designated as either reference or equivalent methods. Accuracy of the subject method is determined by collocating the subject method with a FRM sampler in an urban environment. However, these samplers are not tested in the presence of agriculture dusts, which have a larger mass median diameter (MMD) than urban dusts. This research addressed the performance characteristics of PM₂₅̣ samplers in the presence of agricultural dusts. Tests in a controlled laboratory environment were performed on three PM₂₅̣ samplers: a FRM sampler with Wells Impactor Ninety-Six, a FRM sampler with Sharp-Cut Cyclone, and a High-Volume PM₂₅̣ Sampler. Three dusts were used for sampling: alumina, corn starch, and wheat flour. Ten replications were performed for each sampler in each dust for a total of ninety replications. Performance characteristics, by way of fractional efficiency curves, could not be determined for all of the samplers. The cut-point and slope for the FRM sampler with WINS were found to be 1.95 ± 0.10 [u]m and 1.31 ± 0.04, respectively. Concentration measurements for the test samplers were compared to the "true" PM₂₅̣ concentrations, determined by multiplying the fraction less than 10 [u]m from the Coulter Counter PSD times the TSP concentration. The results showed the percent error of the PM₂₅̣ samplers increased with the MMD of the dust sampled. The hypothesis was that the PM₂₅̣ samplers used to monitor PM₂₅̣ concentrations in the ambient air will not accurately perform in an agricultural environment. It was concluded that the use of these PM₂₅̣ samplers would result in unfair regulation of the agricultural industry.