CARB: CNG emissions need study; clean diesel cleaner than CNG? New CARB study raises questions, draws quick reaction from industry - Emissions - California Air Resources Board - compressed natural gas - Brief Article

Diesel Progress North American Edition, June, 2002 by Mike Osenga

The California Air Resources Board (CARB) said a recent study of bus engines shows that compressed natural gas (CNG) emissions require further study. CARB Chairman Dr. Alan Lloyd said, "The data suggests that both CNG and diesel engines need additional emission controls and with those controls both can achieve substantial and beneficial emissions reductions."

CARB's study showed that the levels of toxic pollutants in CNG exhaust may require further study and may warrant additional control. In what has many in the industry buzzing, the same test showed that a diesel-fueled bus, running on low sulfur fuel, produced lower emissions than either the diesel or CNG baseline buses in total mass particulate matter and the amount of toxic organic compounds. Both types of diesel buses had higher [NO.sub.x] emissions and a particulate filter equipped diesel bus showed a substantial increase in the amount of [NO.sub.x] emitted [NO.sub.2].

The research study tested the buses on a dynamometer from March through June of 2001. Both the diesel and CNG buses were standard New Flyer 40-passenger vehicles powered by Detroit Diesel series 50 engines. The diesel bus was run as a baseline vehicle with a Nelson catalyzed muffler, and with a Johnson Matthey Diesel/CRT particulate filter.

"Both the CNG bus and trap-equipped diesel bus produced lower emissions compared to the conventional diesel bus," Lloyd said. "When the diesel bus was refitted with a trap and run on low sulfur fuel its performance was very promising." Additional tests are now being conducted that will use the same CNG bus refitted with an oxidation catalyst and a new CNG bus equipped with a manufacturer installed oxidation catalyst. Results from those tests are expected by mid-2002. CARB said it also hopes to test a particulate trap on a CNG bus when a suitable trap becomes available.

As expected, industry reaction was swift and split down party lines. The Diesel Technology Forum said the study indicates that California's massive South Coast Air Quality Management District (AQMD) in Los Angeles may have jumped the gun in mandating compressed natural gas (CNG) for buses and other vehicles in its jurisdiction.

Allen Schaeffer, executive director of the Diesel Technology Forum said the CARB study questions the objectivity and wisdom of South Coast District's two-year old CNG-only decision. That policy, based on conjecture rather than comparative data, has seen taxpayers subsidize hundreds of millions of dollars for new CNG vehicles and fueling stations -- in the midst of the natural gas shortage, he said.

Some 13 transit fleets and all school districts in the South Coast AQMD region have been required to direct new purchase dollars to the more expensive, less reliable, and potentially more toxic CNG buses, said Schaeffer. "It's a prime example of why government agencies should not pick winners and losers in the technology arena," he added.

A joint statement issued by the American Lung Association of California, the Coalition for Clean Air, the Natural Resources Defense Council, the Planning and Conservation League, the Sierra Club and the Union of Concerned Scientists, said in part that the study compares "yesterday's natural gas technology with tomorrow's diesel technology -- it's an unfair comparison that fails to represent the true potential for natural gas technology."

The statement added, "despite our concerns about the test methods, we are extremely encouraged to know that new diesel buses can be cleaned up to a point where particulate emissions are very low. We also believe that natural gas buses, using basic pollution control equipment (oxidation catalysts) can achieve even lower particulate emissions than we found with the earlier generations of the technology -- significantly lower than the diesel results in this test.

"We're encouraged that the natural gas bus industry has committed to including oxidation catalysts on the natural gas buses rolling off the production lines today, and that adding those catalysts to the existing natural gas fleet is relatively inexpensive."