Retrofits Can Eliminate Self Pollution, Clean Air Advocate Says

WASHINGTON, D.C. - As the diesel pollution battle rages on, with little indication it will cease anytime soon, a clean air advocacy group says crankcase ventilation systems can virtually eliminated onboard emissions.

The Clean Air Task Force says crankcase filters, along with Diesel Particulate Filters (DPF), would make the nation's school bus fleet not only the safest modes of mass transit but also the cleanest.

Much ink has been dedicated in this space the last several months to the issue of the leaking of harmful diesel fumes inside the cabin, which some say could increase the risk of cancer in students.

In January, the Clean Air Task Force (CATF) - a nonprofit dedicated to restoring clean air and healthy environments through scientific research, public education, and legal advocacy - published a study with similar findings to those of the National Resource Defense Council, the Environment and Human Health Inc. and the California Resources Board that diesel exhaust onboard the school bus is a big problem. A month later, CATF called on the federal government to increase funding for school bus retrofits, and the diesel trucking industry in general.

The CARB-funded study performed by the University of California and described in the June 2005 issue of School Transportation News suggested that children breath in 2.5 times more diesel pollution onboard the bus than adults outside because their lungs are still developing.

The real issue, CATF said, is that upcoming EPA Clean Air guidelines for the use of ultra low sulfur diesel (ULSD) apply only to new engines, with the problem being the number of heavy duty trucks and buses that are already on the road and won't be retired for decades. For the school bus industry, this is measured in self-pollution.

"Our best analysis is the school bus sector contribution to overall PM levels is not the primary issue," said Gordon Schneider, advocacy director at CATF. "Relative to other vehicle categories they are not a huge contributor to ambient levels of PM. Their duty cycles are much more limited, the numbers are much smaller. When we look at school buses we really do focus on the self pollution."

In studying school bus fleets in Ann Arbor, Mich., Atlanta and Chicago in late 2003, Schneider said that CATF found conventional school buses allow a plume of exhaust to roll into the cabin each time the doors open when picking up or dropping off students. By retrofitting the bus with a PM filter and using ULSD, "those two things in combination virtually eliminate that phenomenon."

Additionally, the group recommended reduced idling programs, keeping windows closed during routes and staggering drop-off and pick-up times in front of schools to eliminate a "stacking" effect. CATF did not offer any specifics as to how school districts could implement such measures but added that it is working on identifying possible funding through programs like Clean School Bus USA.

CATF's school bus self-pollution report can be found online at www.stnonline.com/pdf/ catf_self pollution.pdf.

"We're really the first group to significantly look at emissions controls and how they benefit cabin air quality," said L. Bruce Hill, Ph.D., a senior scientist with CATF. "We're trying to flush out the problem. We wanted to investigate for ourselves the cause of pollution where we really care about it."

Hill, Neil J. Zimmerman, an associate professor at Purdue University's School of Health Sciences, and CATF Research Assistant James Gooch found that the most cost-effective initial step for school districts to take is to equip all existing diesel buses with crankcase filtration systems to curb harmful pollutants on board the school bus. Diesel oxidation catalysts, on the other hand, improve ambient air only when the bus is in motion, and at a clip of only 20 percent compared to 90 percent using DPFs.

"It turned out to be a much more interesting study then we ever expected," Hill added. "Old buses that pollute more, you're going to get more pollution in the cabin no doubt. But even newer buses without controls still see onboard emissions."

CATF estimated that 13 million existing diesel engines are on the road. Assuming that all 500,000 school buses nationwide needed similar retrofits, argues a former U.S. EPA attorney, it could cost the industry as much as $3.5 billion. Michael Gibson, now practicing with law firm Jones Day in Houston, added in his refutation study, "Taking the Clean Air Task Force to Task for Junk Science: Diesel Exhaust and Health Effects," that CATF accounts for diesel fleets to be in operation for 30 year cycles, which is based on a 15-year-old duty cycle study performed by the U.S. Department of Energy. In actuality, most fleets now display an average life of 12 to 13 years.

But, in the school bus world, Gibson said the majority of school bus ages remain a far cry from the 30-year figure cited by CATF.

Schneider replied that the 30-year figure is only intended for heavy-duty, on-highway diesel trucks, which are the worst ambient air polluters. The duty cycles for school buses are much more limited, he said, and the numbers are much smaller making onboard self pollution the industry's biggest problem.