Many businesses and industries use stationary internal combustion engines to run or augment their processes. Engines may be either compression or spark ignition, and emit various key pollutants regulated under the National Emission Standards for Hazardous Air Pollutants 40 CFR 63 Subpart ZZZZ, often called the 4Z rule. Other engine air quality rules include two New Source Performance Standards, NSPS. The 4I NSPS applies to compression ignition engines and the 4J NSPS applies to spark ignition engines.
Combustion portal provides basic engine compliance and pollution prevention information. This resource is supported by the National Compliance Assistance Centers.