The Clean Air Act authorizes EPA to control emissions from stationary sources of air pollution. EPA regulates stationary engines through two types of regulations:

• National Emission Standards for Hazardous Air Pollutants (NESHAP) – which regulate emissions of hazardous air pollutants (or HAPs) from new, existing and modified sources. These standards require application of technology-based emissions standards referred to as Maximum Achievable Control Technology (MACT).
• New Source Performance Standards (NSPS) – which regulate emissions of criteria pollutants from new, modified and reconstructed sources. These standards require initial performance testing and ongoing monitoring to demonstrate compliance with established standards for that source category.

There are currently three regulations that apply to stationary engines:

• NESHAP for Reciprocating Internal Combustion Engines (RICE)
• NSPS for Stationary Compression Ignition (CI) Internal Combustion Engines
• NSPS for Stationary Spark Ignition (SI) Internal Combustion Engines