8 December 2000

In its hearing on December 7-8 in Sacramento, the California Air Resources Board (ARB) approved the Lower-Emission School Bus Program guidelines. The program will provide grants for school districts to retrofit existing school buses with diesel particulate filters, to purchase new clean diesel buses, and to purchase new natural gas buses. By dividing the funds evenly between the diesel and natural gas technologies, the ARB has recognized the emission benefits of modern diesel engines coupled with particulate filters.

The ARB approved $12.5 million for purchases of new buses using clean diesel technology, $12.5 million to retrofit old buses with particulate filters, and $25 million to purchase new buses powered by natural gas.

New buses funded under the program have to meet the following requirements:

  1. Alternative fuel (natural gas) buses have to be certified to the ARB’s optional, reduced-emission NOx standard of 2.5 g/bhp-hr and a PM emission level of 0.03 g/bhp-hr
  2. Diesel buses have to meet a 3.0 g/bhp-hr NOx level and a 0.01 g/bhp-hr PM level. Although the 3.0 g/bhp-hr NOx diesel buses do not meet the ARB’s optional, reduced-emission NOx standards, the ARB considers them an intermediate step allowing for the introduction of lower-emission diesel engine technology. They would need to be certified to a federal engine family emissions limit (FEL) of 3.0 g/bhp-hr NOx. They would also be required to use low-sulfur diesel fuel.

School districts would be required to provide 25% of the cost of the new bus, up to a maximum of $25,000, as match funding. The state would pay a minimum of 75% of the cost of the bus.

The retrofit part of the program involves installation of particulate filters on existing, older diesel buses and operating the buses using ultra low sulfur fuel (15 ppm S). The adopted funding level will allow to retrofit more than 1500 buses, out of the 24,000 statewide fleet. The program will cover the entire cost, including the filter, its installation, and $500 to cover the incremental cost of ultra low sulfur fuel (estimated at 3-5 cents per gallon).

Particulate filters used for the program have to be certified by the ARB to achieve an 85% conversion efficiency on the transient FTP test cycle. The certification process also requires a complete demonstration of durability and effectiveness, and requires manufacturers to warrant their retrofit devices for 150,000 miles (an estimated 10 year period) for emissions effectiveness and for 100,000 miles for mechanical performance.

The ARB decision and allocation of funds was applauded by Navistar International Corporation, a major supplier of diesel engines used in school buses. Navistar has been developing a low emission diesel engine package for school buses, known as “Green Diesel Technology”, which utilizes advanced engine technology fitted with a catalytic diesel particulate filter.

“Thanks to advances in diesel technology, clean diesel has become a significant part of the clean air solution in California”, said Tom Trueblood, manager of public affairs for International Truck and Engine Corporation. While substantially reducing air pollution, the new clean diesel technology is less expensive than costly natural gas systems. “This appropriation will benefit school districts that recognize the economic and environmental benefits of Green Diesel Technology”, Trueblood said.

Navistar said, it will bring to market in mid-2001 a new smokeless and odorless diesel school bus fueled by ultra-low sulfur fuel, and equipped with a particulate filter and a special low-NOx engine calibration. The bus will be certified to the 3.0 g/bhp-hr NOx and 0.01 g/bhp-hr particulate matter standards, as required by the ARB.

Source: California ARB | Navistar