Ag Engine Registration

The District is required by the California Air Resources Board (ARB) to register agricultural engines rated at greater than 50 horsepower (excluding mobile equipment such as tractors, harvesters, bailers, or spray rigs) sited in the District (map note: this could be a hyperlink). These engines are most typically used for stationary or portable water pumps or running a portable compressor or electrical generator.

Engines must meet emission requirements established in State law. Older diesel engines (which have been regulated since 2009) must be replaced over time, with sunset dates phasing in between 2010 and 2015.  Currently, new engines must be EPA-certified Final Tier 4 engines. Engines purchased to replace older registered engines must be EPA-certified Tier 3, Interim Tier 4 or Final Tier 4 engines. Propane engines must also be registered with the District.

Exceptions are reviewed on a case-by-case basis when Final Tier 4 engines are not available in the size and configuration needed.

Intermittent- and Low-Use Engines

Our District Board of Directors adopted provisions in 2010 to allow those older registered engines which were reaching their sunset dates to get a little additional useful life by converting over to intermittent-use or low-use status, provided they meet District requirements. Under both categories, the engine must be sited at least a half-mile from any residential area, school or hospital and must have been registered by Yolo-Solano AQMD continuously since prior to March 8, 2011.

Intermittent-Use: The engine can run for only 2,000 total hours (not to exceed 10 calendar years) under intermittent-use registration before being retired.

Low-Use: The engine can run no more than 200 hours in any one year and a total of 2,400 hours under low-use registration before being retired.

How to Apply 

The Ag Engine Registration Form and Master Fee Schedule is available on our Applications & Forms page.

How to Cancel a Registered Engine 

The ag engine cancellation request form is available on our Applications & Forms page.


The ARB- adopted rules on emissions limits for ag engines in 2005 and 2006. These rules required local air districts to develop registration programs for these engines. The Yolo-Solano AQMD Board of Director created the District’s program in 2008 by adopting Rule 11.3.

The intent of the program is to ensure ag engines in Yolo and northeastern Solano meet state emission guidelines. Diesel exhaust is a carcinogen, and diesel engines produce fine particulate pollution, a pollutant the Yolo-Solano AQMD is required to monitor for and for which state and federal health standards have been developed.