Clean Air

Rich Burn

Spark ignited engine where the manufacturer’s recommended operating air/fuel ratio divided by the theoretical air-to-fuel ratio required for complete combustion at full load conditions is less than or equal to 1.1. [Source: Code of Federal Regulations, Title 40, Part 63.6675.]


An area that does not meet (or that contributes to ambient air quality in a nearby area that does not meet) the national primary or secondary ambient air quality standard for the pollutant established by the U.S. Environmental Protection Agency pursuant to the federal Clean Air Act [as amended].  [Source: California Air Resources Board website:] …

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Lean Burn

A “lean burn” engine uses a relatively lean amount of fuel in the engine’s combustion chamber. On a comparative basis, lean burn engines use less fuel than “rich burn” engines, thereby producing fewer emissions per unit of output. (The Code of Federal Regulations, Title 40, Part 63.6675, defines “lean burn” engines as any engine that …

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Criteria Pollutant

A pollutant determined to be hazardous to human health and regulated under EPA’s National Ambient Air Quality Standards.  [Source: EPA website:]

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