The Utah Air Quality Board unanimously approved the revisions Wednesday.

To qualify, a vehicle must have been built by the manufacturer to use cleaner-burning fuel, such as natural gas. Otherwise, converted vehicles require lower emissions as defined in the U.S. Environmental Protection Agency's certification program.

The state Division of Air Quality's Mat Carlisle told the board Wednesday that EPA certification is important to ensure converted vehicles are cleaner, comply with federal emission standards and don't conflict with local emission programs.

Converted vehicles that do not meet the certification do not qualify for the credit, he said. But some people still are making the switch because of the high cost of gasoline.

"This has become an issue," said DAQ Director Cheryl Heying.

Another problem, Carlisle added, is that some people are importing used, natural-gas cars from other states and applying for credits worth a few thousand dollars here, credits worth more than the car.

fahys@sltrib.com

The clean-fuel tax credit

* The Legislature created it in 1992.

* The fund has paid out $4.1 million since 2002.

* Seventy-three people claimed the credit in 2002.

* In 2007, the number had grown to 663.