Environmental lands DepartmentDiesel School Bus Retrofit Project

Diesel is the world’s most efficient internal combustion engine returning 20-40% more miles per gallon than comparable gasoline engines. Due to its inherent efficiency, the diesel engine is the predominant power source for many important sectors of the economy. This includes freight transportation, public transportation (school buses), and off road vehicles used in agriculture and construction however...

Diesel is one of the largest sources of fine particle pollution with estimations showing that 1/3 of Minnesota’s air pollution comes from “Mobile Sources" (diesel powered machinery and/or vehicles).

  1. Fine particles like those found in diesel exhaust cause 15,000 premature deaths each year.
  2. Diesel fueled engines also emit nitrogen oxides that form ground level ozone (smog).
  3. The major components that contribute to pollution
    from diesel engines include;
    • Carbon Dioxide (CO2)
    • Carbon Monoxide (CO)
    • Nitrogen Oxide (NOx)
    • Particulate Matter (PM)
    • Formaldehyde
    • Benzene
    • PAH’s

School buses provide 24 million children with transportation to and from various school activities every year. Air inside buses is 5 times more polluted than the air outside of the bus. This is harmful because:

  • Children can spend more than an hour to two hours on a bus each day to and from school.
  • Children have a much faster breathing rate than adults, about 2 gallons per minute.
  • Diesel emissions have been known to cause lung damage, respiratory problems, and exacerbate asthma and existing allergies.

Steps are being taken and progress made to protect our children and environment to reduce the amount of emissions that are given off by school buses.

1. Better idling practices.

  • Idling wastes fuel and money. A typical school bus burns one half gallon of diesel fuel for each hour of idle time.
  • It is estimated that if a fleet of 50 buses reduces its idle time by 30 minutes per day, at 1$ per gallon of diesel fuel, the entire fleet would save 2,250$ per school year in fuel costs.

2. Use cleaner burning fuels.

  • Bio-Diesel: Using vegetable oils to produce diesel fuel. Can be used at 100% or blended with regular diesel to decrease emission and burn cleaner.
  • Ultra low sulfur diesel: has an extremely low sulfur content (15 parts or less per million) and has been required nation wide since the beginning of 2006.
  • Emulsified diesel: a blended mixture of diesel, water and other additives used to reduce the emissions of particulate matter and nitrogen oxides (NOx).

3. Retrofitting area school buses with pollution control equipment.

Diesel Oxidation Catalyst (DOC): The most commonly used retrofitting technologies today. They are relatively simple, low cost, can be installed in almost all buses and require very little maintenance. Oxidation Catalysts can be used with regular diesel fuel and typically cost between 5000$ and 10,000$. This method of retrofitting reduces particulate emissions by 20-30%. Reductions will be greater if used with an ultra low sulfur diesel fuel.

Particulate Matter Filter: Provides the most efficient particulate matter reduction. The filter has a more complex technology and is most appropriate for the 1995 and newer buses. The cost for this filter is between 5000$ and 10,000$ and require the use of ultra low sulfur diesel fuel. This method of retrofitting, with the combination of ultra low sulfur diesel fuel, reduces particulate emissions 60% to 90%.

4. Replace the oldest running buses with new ones. (Legacy Fleet)

  • About 1/3 of school buses being used today were built before 1990 and are not up to speed with today’s retrofitting pollution control methods.
  • Pre-1990 buses can pollute as much as six times more than today’s newer buses. Because they are not equipped with today’s pollution control features they are excellent candidates for replacement.


On August 29th 2006 the Leech Lake Band of Ojibwe Air Program hosted a one day all day community workshop on reducing diesel emissions and health effects in Cass Lake, Minnesota. Another workshop is being planned for August 2007,

Information shared at the workshop was:

  • health issues related to diesel emissions
  • diesel engine technologies
  • diesel retrofit equipment
  • diesel fuel technologies
  • regulatory issues
  • voluntary grant initiatives

The main objective of our workshop was to discuss the effects of diesel emissions, to dispel misinformation, and to show the community that this is something that we can do together to improve our immediate air quality.

Through our community-based efforts we successfully involved:

  • Riggles Bus Company – Cass Lake/Bena School District
  • Nortran Bus Company – Deer River School District
  • Laporte School District
  • Bemidji School District
  • Northland Community School – Longville-Remer School District
  • Bug-O-Nay-Ge-Shig Tribal School
  • Project Green Fleet
  • Leech Lake Air Program


Project Green Fleet of Clean Air Minnesota was extremely exited to hear of such a movement at the grassroots level that they were willing to assist in funding the project. In May of 2007 the Leech Lake Diesel Retrofit Project (Phase I, including 4 school districts) was approved for full funding of all buses from the four participating school districts. This means up to 112 buses may be retrofitted depending on their age, manufacture, and lifespan. Currently the Leech Lake Air Program is in process of Phase 2 of the Diesel Retrofit Project looking for other nearby school districts to join Phase 2 of the project and be potentially funded by Project Green Fleet or other grant initiatives.

Contact Us


Name Title Phone
Brown, Levi Environmental Lands Director (218) 335-7417
Toft, Brandy Air Quality Specialist (218) 335-7429
    1-800-442-3922 Toll-free
    (218) 335-7430 Fax