Diesel exhaust is emitted from a bus's tailpipe, of course, but also from a vent on the engine. Tests have shown that when a bus stops and opens its door wind can blow fumes inside the bus. Diesel engines became cleaner in 2004 and they'll improve significantly in 2007 and ultra low sulfur diesel fuel is also much cleaner and will be more available later this year, but school buses can last for decades. There are two solutions, retire older buses sooner or install filtering devise on the engine and tailpipe. Betin Santos is with Environmental Defense and is Director of Houston Clean Air for Life Program.
"There are certain school districts within the area, you've got Conroe ISD and also Houston ISD, which have been working on this for a few years."
She there are over just over 7500 busses in this area about 10% have been retro-fitted or replaced early. She says 10% is higher percentage then the statewide average. And least you think this is a hard sell, Santos says she's been very impressed with local school districts.
"If they can find the money to do it then they are certainly willing to do it."
Environmental Defense is conducting a five city study and a main goal is to help schools get grants to pay for new cleaner busses or to retro-fit older ones. The Conroe School District used $745,000 in grants to clean-up its older buses. Sam Davila is the district's Transportation Director.
"We have 315 large buses, or what people call big buses which are 71 passengers. Retro-fitted with the diesel particulate filters we have 112. Now the new buses that have the 2004 compliant engine or better we have 75 of those."
One scientist with the study said the Conroe fleet is cleanest he's seen. That's because the filters really work. Dr. Bruce Hill is chief scientist with Clean Air Task Force. He's behind an older Conroe ISD bus with a hand held meter that measures the fine particulate that diesel engines emit. This bus does not have a tailpipe filter,
"I'm about a foot away from the tailpipe and I can see the levels coming out of the exhaust pipe are about 200 times the outdoor air. It's these emissions that get into the school bus through the cabin door. When we go to the retro-fitted bus you'll see that these numbers are similar to the outdoor air, that the filter actually removes all of these particles that we're measuring right now."
A similar demonstration shows the same result for emissions from the engine vent. And the tests show that buses with both filters are actually cleaner then the new 2007 standard buses will be.
Next week we'll find out more about how tests are conducted to measure how and how much particulate matter gets into school buses.