On April 6, 1983, the United States Environmental Protection Agency (EPA) proposed a standard under Section 112 of the Clean Air Act limiting airborne polonium-210 emissions for calciner operations at domestic elemental phosphorus plants to 1 Ci/yr. To evaluate the effect of the proposed standard, physical and chemical properties of polonium through plant processes assessed. Results indicate that polonium is volatilized from phosphate ore during calcining and, for the most part, deposited on fine particulates leaving the process. Projected emissions for each elemental phosphorus plant were determined using available data, and the uncertainty associated with each estimated release was evaluated. After taking into account this uncertainty, two plants were determined to exceed the proposed limiting standard for airborne polonium emissions. One plant was found in borderline compliance. Emission control alternatives are proposed for the three plants. Cost estimates associated with each proposed alternative are provided.