The report has been prepared to provide information on phosphoric acid manufacture by the thermal process. This report does not include information on the manufacture of phosphoric acid by the wet process. Background information is included to define the importance of the thermal-process phosphoric acid industry in the United States. Basic characteristics of the industry are discussed, including growth rate in recent years, uses for the product, and the number and location of the producing sites. A process description is given for the thermal process. Process information includes discussion of normal process variables that affect the quantity of emissions, the normal range of emissions, and methods of controlling or reducing emissions. Supplemental material provides detailed emission sampling and analytical methods. Emissions to the atmosphere from a thermal-process phosphoric acid plant depend upon a number of factors, such as plant design, skill of operation, efficiency of hydration, and the type and operation of special devices to reduce emissions. (Author)