API Publ 4720 pdf download.Comparison of API and EPA Toxic Air Pollutant Emission Factors for Combustion Sources 2 COMPARISON OF PUBLISHED EMISSION FACTORS The two primary sources of published emission factors for air toxics from combustion processes are the EPA’s AP-42 document and the API’s Petroleum Air Toxics Emission Factors (PATEF) database. The EPA periodically updates emission factors to incorporate...