Method for determining the crustal fraction of particulate matter emissions from cattle feedlots
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The EPA considered excluding the crustal component of particulate matter (PM) in the course size range of 2.5 to 10 micrometers AED for agriculture and mining PM emissions (USEPA, 2006a). It was reported that public exposure to concentrations of PM in the crustal fraction of the PM coarse (PMc) emitted from agricultural sources were not associated with health effects. The final version of 40 CFR 50 (USEPA, 2006b) did not include an exclusion for the crustal fraction of PMc. EPA defines the crustal fraction of PMc as PMc derived from soil. If the crustal credit were to be put into effect, all agricultural facilities including cattle feedlots would likely benefit. For example, if a cattle feedlot were required to meet an off-property PM10 concentration of no-more-than 150 g/m3 (NAAQS) and had a measured or modeled downwind concentration of 200 g/m3, then would have to put abatement strategies into place. However, if it were determined that fifty percent of the PM10 was crustal, the cattle feedlot could be given a fifty percent credit and would likely be regulated based on 100 g/m3. Currently, there is no objective scientific method for quantifying the mass fraction of crustal in the measured or modeled PM concentrations. Historically, PM speciation studies have focused on urban PM sources which are dominated by the fine particles (particles less than 2.5 micrometers). More speciation data are needed for agricultural sources in order to obtain credit for the crustal fraction. More importantly a standard methodology is needed in order to determine the percentage of crustal material downwind from an agricultural source. This paper outlines the protocol to be used for determining a definition of the crustal fraction of PMc as well as the methodology to determine the mass fraction of crustal in the PMc emissions from cattle feedlots.
