NRDC: No Breathing in the Aisles: Diesel Exhaust Inside School ...

The “green” diesel
engine will emit 1.6 to
1.7 times more NOx
than its natural gas
counterparts.
the CARB diesel. 107 Finally, levels of toxic air contaminants such as benzene, toluene,
1,3-butadiene, formaldehyde, and polycyclic aromatic hydrocarbons (PAHs) were not
significantly reduced by use of the newer diesel fuel. 108 Thus, even the most advanced diesel
engine available, with California reformulated diesel fuel, remains far from clean.
The bottom line is that alternative fuel school buses, such as natural gas, are much cleaner
than currently available diesel school buses in terms of air toxics, NOx, and PM emissions.
Diesel engine technology will continue to improve in emissions performance with advanced
engine modifications and the use of aftertreatment, but alternative fuel technology will also
take advantage of these advances and retain its clean lead over diesel.
International Truck’s proposed “green” diesel school bus is still dirtier than
a comparable natural gas bus
In January 2000, International Truck Company and Engine Corporation (International)
introduced its so-called “green” diesel school bus, which has lower NOx and PM emissions
than currently certified diesel engines as a result of optimized engine calibration and the use
of a particulate trap designed to run on ultra-low sulfur fuel (5 ppm or less). While this school
bus has not yet been certified, International is hoping to have the bus available for sale in
August 2001. International claims that its new “green” diesel engine will achieve reductions
of 25 percent in NOx and 90 percent in PM emissions over current heavy-duty diesel engine
standards. While the advancements of International’s “green” diesel engine technology
promise a marked improvement over current certified diesel engine models, “green” diesel
engines still will not be as clean as currently available and certified alternative fuel engines.
First, as Table 5 shows, the “green” diesel engine will emit 1.6 to 1.7 times more NOx than
its natural gas counterparts. Second, there is some uncertainty over whether the “green”
diesel engine will be able to reach even its projected NOx and PM emission targets, because
the engine was originally designed to run on ultra-low sulfur diesel fuel (5 ppm or less) which
is not available anywhere in the United States. In December 2000, EPA adopted regulations
requiring a reduction in sulfur content in diesel fuel nationally to 15 ppm by 2006 – but
neither EPA nor California has proposed to lower the sulfur content any further or any earlier.
Two refiners, British Petroleum (BP) and Equilon Enterprises (also known as Royal
Dutch/Shell Group), have made commitments to make low-sulfur diesel fuel (at 15 ppm)
available to California school bus fleets upon request by 2002. 109 BP has also made
commitments to deliver 30 ppm sulfur diesel to the Houston, Texas metropolitan area. 110 In
addition, some 30 ppm sulfur diesel fuel is available in New York City courtesy of Tosco. 111
Absent a regulation requiring the sale of low-sulfur fuel on an expedited basis, however,
additional capital investments to produce and provide low-sulfur diesel on a local, regional, or
national scale are not expected to be made by refiners until 2006. 112
Beyond fuel quality and availability issues, substantial concerns remain as to the durability
and in-use performance of PM aftertreatment equipment for the full useful life of a school
bus. Currently, data on in-use emissions and durability performance for PM aftertreatment is
extremely limited for school buses, making it unclear as to whether these technologies will
continue to achieve a lower emissions performance in the real world. In fact, we estimate,
30