Federal, state, and local stack and automobile exhaust emission limits that regulate the quantity, rate, or concentration of emissions. Emission standards can also regulate the opacity of plumes of smoke and dust from point and area emission sources. They can also assess the type and quality of fuel and the way the fuel is burned, hence the type of technology used. With the exception of plume opacity, such standards are normally applied to the specific type of source for a given pollutant. Federal standards include New Source Performance Standards (NSPS) and National Emission Standards for Hazardous Air Pollutants (NESHAPS). Emission standards may include prohibitory rules that restrict existing and new source emission to specific emission concentration levels, mass emission rates, plume opacity, and emissions relative to process throughput emission rates. They may also require the most practical or best available technology in case of new emission in pristine areas.
New sources and modifications to existing sources can be subject to new source permitting procedures which require technology-forcing standards such as Best Available Control Technology and Lowest Achievable Emission Rate (LAER). However, these standards are designed to consider the changing technological and economic feasibility of evermore stringent emission controls. As a result, such requirements are not stable and are determined through a process involving discretionary judgements of appropriateness by the governing air pollution authority.
See also Point source