DIAMOND BAR, Calif. -- The South Coast Air Quality Management District (SCAQMD) remains poised to vote on its Proposed Rule 1195-Clean On-Road School Buses, despite EPA and CARB certification of clean diesel engines, based on low-sulfur diesel fuel, in California.

Proposed Rule 1195 would require school bus fleet operators to purchase CNG models when acquiring new buses, unless outside funds are unavailable to cover the $30,000 cost of a CNG bus over clean diesel alternatives, and unless at least $8,000 is not available to pay for a CNG fueling station.

The measure would apply to some 8,800 school buses in the SCAQMD's three-county region - about 3,700 operated by school districts, 4,900 operated by private firms and 200 by private schools.

This year, $22 million is available to operators under SCAQMD regulation for the purchase of lower-emission school buses, including $16.6 from California's $50 million Lower-Emission School Bus Program. The California Air Resources Board (CCARB) has ruled that school buses fueled by either clean diesel or CNG are eligible for subsidy under the state program, giving operators throughout California a choice between the two alternatives to conventional diesel. The SCAQMD is the only one of 15 air management district in the state seeking to limit OEM school bus purchases to CNG only.

For more than a year, the clean diesel engine technology that has been at the center of this controversy has been International Truck and Engine's Green DieselT technology, that uses low-sulfur diesel in conjunction with particulate traps. It is currently the only such engine certified in California to date.

Although recent studies point to some advantages of clean diesel over CNG, including safety, fuel efficiency and cost, the SCAQMD supports its proposal by citing its 1999 Multiple Air Toxics Exposure Study II, which concluded that conventional diesel exhaust is responsible for about 71% of total cancer risk posed by all air pollutants. The air district does note that while green diesel buses emit a 27 percent higher NOx, particulate emissions are less than that of CNG buses. It fails to add that NOx emissions of clean diesel are 83% lower than those of 1988 conventional diesel. And, while the SCAQMD also notes that there are currently close to 40 CNG fueling stations accessible to the public - only some of which are capable of fueling full-size buses, while some such as the one in Torrance, Calif. closed recently - it is silent on the number of fueling stations capable of supplying low-sulfur diesel fuel.

The SCAQMD's position was bolstered recently when the school board of the Los Angeles Unified School District voted to ban future purchases diesel engine school buses.

The SCAQMD, manages air pollution control for urban portions of Los Angeles, Orange County, and San Bernardino and Riverside counties, is scheduled to vote on Proposed Rule 1195 on April 20.