Estimating FRM PM10 Sampler Performance Characteristics Using Particle Size Analysis and Collocated TSP and PM10 Samplers: Cotton Gins

Abstract

In the U.S., regional air quality compliance with national ambient air quality standards (NAAQS) for particulate matter (PM) is based on concentration measurements taken by federal reference method (FRM) samplers. The EPA specifies the performance criteria for the FRM samplers. These criteria for the FRM PM10 samplers are defined as a cutpoint and slope of 10 ±0.5 µm and 1.5 ±0.1, respectively. It is commonly assumed that the performance characteristics of the FRM PM10 sampler do not vary and are independent of the PM characteristics. Several sources have observed errors in the concentrations measured by the FRM PM10 samplers and have suggested that shifts in the sampler performance characteristics may lead to the observed concentration measurement errors. Limited work has been conducted on quantifying the shift in the performance characteristics of the FRM PM10 sampler operating under field conditions. Recent work at a south Texas cotton gin showed that true PM10 concentrations were 55% of the concentrations measured by the FRM PM10 sampler. If the FRM PM10 sampler were operating within the performance criteria range specified by the EPA, then the true concentrations would be within approximately 12% of the concentrations measured by the FRM PM10 sampler. The focus of this work was to quantify the shifts in the cutpoint and slope of the penetration curve of the FRM PM10 sampler. Results show that the cutpoint and slope of the FRM PM10 sampler shifted substantially and ranged from 13.8 to 34.5 µm and from 1.7 to 5.6, respectively, when exposed to large PM as is characteristic of agricultural sources. These shifts in the cutpoint and slope of the FRM PM10 sampler resulted in overestimation of true PM10 concentrations by 145% to 287%.