Which of the following best describes the purpose of AP-42?

• A. It lists soil sampling protocols.
• B. It provides a framework for measuring water discharges.
• C. It is a testing protocol for groundwater.
• D. EPA's Compilation of Air Emission Factors used to estimate emissions and support regulatory modeling and permit actions.

Answer: (C)

AP-42 is EPA’s Compilation of Air Emission Factors, a reference that provides published emission factors to estimate air emissions from a wide range of sources. The core idea is to convert an activity level—such as fuel usage, material processing, or hours of operation—into an expected amount of pollutant released, by multiplying the activity rate by an emission factor. These factors come from tests, measurements, and modeling studies and cover many source categories, from combustion to industrial processes to fugitive emissions. This standardization lets regulators and facilities estimate emissions for regulatory modeling, permit applications, and compliance demonstrations without needing new, case-by-case measurements for every situation. It’s not about soil sampling, water discharge frameworks, or groundwater testing protocols—those address different environmental topics.