ABSTRACT

The regulation of particulate matter (PM) emitted by agricultural sources (cotton gins, feed mills, concentrated animal feeding operations (CAFOs) is based upon downwind concentrations of particulate matter less than 10 and 2.5 micrometers (µm) (PM₁₀ and PM_2.5) aerodynamic equivalent diameter (AED). Both PM₁₀ and PM_2.5 samplers operate by pre-separating PM larger than the size of interest (10 and 2.5 µm) prior to capturing the PM on the filter. It has been shown that Federal Reference Method (FRM) PM₁₀ and PM_2.5 samplers have concentration measurement errors (Buser et al, 2001, 2002) when sampling PM in ambient air having mass median diameters (MMD) larger than the size of interest. It has also been demonstrated that most PM from agricultural sources typically have particle size distributions with MMDs larger than 10 µm (AED). The PM₁₀ concentration measurement error can be as much as 343% for ambient PM with an MMD=20 µm. These errors are a consequence of the PM₁₀ pre-separator allowing a larger mass of PM greater than 10 µm to penetrate to the filter than the mass of PM less than 10 µm captured by the pre-separator. The mass of the particles greater than 10µm that are allowed to penetrate to the filter, introduce a substantial error in the calculated concentration of PM₁₀. Pargmann et al (2001) reported that sampling PM larger than 2.5 µm (AED) resulted in a shift in the cut-point of the pre-separator. If this is true for all PM₁₀ and PM_2.5, samplers, the resulting errors in measurements of ambient concentrations could be even larger than those reported by Buser.

One solution to this problem is to measure the concentration of total suspended particulate matter (TSP) and calculate the concentration of PM₁₀ by determining the mass fraction of PM less than size of interest from the particle size distribution (PSD). The "standard" high volume (TSP) sampler operates at a volume rate-of-flow in excess of 40 cubic feet per minute (cfm) (EPA, 1987b). Most of the current PM₁₀ and PM_2.5 samplers operate at one cubic meter per hour (cmh). (1 cmh = 0.589 cfm.) McFarland (1983) reported that TSP samplers have a "cut-point" of a nominal 45 µm (AED). EPA specifies the engineering design parameters for TSP samplers in 40CFR Part 50 (1987b). This paper reports the engineering design and evaluation of a low-volume (0.589 cfm) TSP sampler (TSP_LV). The results suggest that this new TSP_LV may be more robust and more accurate that the "standard" high volume (TSP) sampler.