What is AP-42?

• A. EPA's Compilation of Air Emission Factors used to estimate emissions and support regulatory modeling and permit actions.
• B. A weather model.
• C. A regulation governing noise emissions.
• D. A protocol for soil sampling.

Answer: (A)

AP-42 is the EPA's Compilation of Air Emission Factors, a reference that provides emission factors—typically expressed as pounds of pollutant per unit of activity—used to estimate emissions from various stationary sources. This resource lets you convert activity data (like fuel usage, material throughput, or production hours) into estimated emissions for pollutants such as NOx, SO2, PM, and volatile organic compounds. The factors come from measurements and engineering studies and are used in regulatory modeling, inventories, and permit actions to assess and control air quality impacts. It’s not a weather model, not a noise regulation, and not a soil sampling protocol.