The EPA is considering the exclusion of the crustal component of particulate matter emissions from agricultural sources. For example, if a cotton gin has a measured downwind concentration of 200 μg/m³ and it was determined that fifty percent of the particulate matter is crustal, then the cotton gin would be given a fifty percent credit and would only be regulated based on 100 μg/m³. Historically, speciation studies have focused around urban sources. More data is needed for agricultural sources, such as cotton gins, in order to apply the crustal exclusion. More importantly a standard methodology is needed in order to determine the percentage of crustal material downwind from a cotton gin. This paper will establish a definition of crustal material as well as provide the methodology to determine the crustal percentage in particulate matter emissions from cotton gins.