CARB Bus Emission Tests Show Natural Gas Still Benchmark for Cleanliness

SACRAMENTO, Calif.--April 18, 2002--Test results released today by the California Air Resources Board (CARB) demonstrate that inherently clean natural gas bus technology is still the yardstick by which heavy-duty engine emission performance is measured. However, the limited testing undertaken by CARB compares yesterday's natural gas technology to tomorrow's diesel technology, according to the California Natural Gas Vehicle Coalition.

CARB compared a single diesel bus, using ultra-low-sulfur diesel fuel and advanced, state-of-the-art emission control equipment, with a natural-gas bus that deployed no emission controls. The agency consequently reported greatly improved results for particulate emissions from the highly controlled diesel engine. While the results for particulate emissions were encouraging, the advanced diesel bus continued to show much higher emissions of nitrogen oxides (NOx), a major contributor to the severe ozone problem facing much of California.

``We are also very concerned that many diesel engines cannot be retrofitted to take advantage of the advanced technology used to gain these results,'' said Sean Turner, the president of the California Natural Gas Vehicle Coalition. ``While these test results are encouraging, they also show that it will be some time before there will be a practical impact that will benefit the public.''

Advanced diesel emission control equipment used in this study can only be applied to 1994 or newer buses using low-sulfur diesel fuel, and cannot be used with two-stroke diesel engines.

``This comparison might be valid if the natural gas engine producers were not already equipping engines with pollution controls, but the fact is -- they are,'' said Michael Eaves, chairman of the California Natural Gas Vehicle Coalition. ``The natural gas industry is committed to being the cleanest transportation fuel, and we are working continually to improve our engines so that all Californians can benefit.''

The latest generation of natural gas transit bus engines (Cummins Westport C-Gas-Plus & the John Deere 8.1) are already using oxidation catalysts to control particulate and toxic emissions. Those engines are already meeting California's extremely stringent 2007 transit bus PM standards (0.01 g/bhp-hr). Furthermore natural gas buses do not require the significantly more complicated and expensive particulate traps and boutique fuel necessary for diesel engines attempting to meet the standard.

``Our existing transit engines already use oxidation catalysts and beginning next year, every one of our natural gas engines will employ advanced aftertreatment devices to ensure that ours remain the cleanest engines available in the heavy-duty marketplace,'' said John Deere's business manager for natural gas engines, Glen Chrusciel

The head-to-head comparison between the trap-equipped diesel bus using ultra low sulfur diesel fuel and a natural gas engine not equipped with the latest pollution control technology is of limited value -- yet the need for state-of-the-art emission reduction equipment is obvious. If California is going to get maximum emission reductions from the heavy-duty fleet, natural gas and diesel are going to have to continue to use the latest emission control technologies available, according to CNGVC.

Because of multiple concerns raised about the initial testing, CARB has agreed to go back to their laboratory to test the emissions of today's catalyst-equipped natural gas engines to augment their own transit bus emission test program. Emissions testing on natural gas buses using oxidation catalysts will begin in Los Angeles on Monday, with results expected by late summer.

Nearly 2,000 natural gas buses already are operating on California roads, and another 800 are on order. The California Natural Gas Vehicle Coalition represents more than 40 natural gas fuel providers, automobile and engine manufacturers, technology companies, vehicle dealers, fleet operators, and public agencies that support the deployment of natural gas vehicles to improve air quality and energy security in California and the U.S.