Project Description

The Missouri Department of Natural Resources was awarded a grant to develop a school bus air emission inventory for Missouri. This grant ended in 2010.

The Central States Air Resources Agency and the U.S. Environmental Protection Agency’s Blue Skyways Collaborative awarded the grant. Department staff used the $64,829 award to develop a school bus emission inventory. This tool will assist the department in achieving the long-term goal of reducing the harmful emissions produced by diesel school bus fleets as they contribute to the formation of ground-level ozone, an air pollutant of concern in Missouri.

The inventory includes for each district the amount of buses in operation, the amount of emission control equipment installed for each school district, any idling policies the school district practices and the amount of diesel emissions emitted by each school district’s fleet. The inventory is based on the Department of Highway Patrol's School Bus Safety Inspection Data from 2009. The compiled inventory is available in the Data and Figures section below.

Project Purpose

Unnecessary idling of diesel school buses wastes fuel and results in avoidable amounts of air toxics being emitted into the air. These emissions further contribute to air quality problems and related health impacts, especially in areas already struggling to meet the recently strengthened National Ambient Air Quality Standards for ozone. By using this funding to acquire average idling times for buses along with information about idle reduction policies being implemented by districts, simple outreach programs can be created with the goal of informing fleets with excessive or unnecessary idling of the impacts that idling has on fuel cost and air quality.

Data and Figures

Missouri School Bus Inventory

Generally diesel emissions can be broken into five different categories of pollutants. These five categories include oxides of nitrogen, hydrocarbons, carbon monoxide, carbon dioxide and particulate matter. Each of these five pollutants have various negative effects on the environment and public health. This emission inventory below includes the ton per year emissions of each of these pollutants in each county of the state that result directly from school bus operation.

Emission Inventory by County

Policies Referenced in Inventory
Voluntary Interdistrict Choice Corporation

Idling Effects on Fuel Costs
The unnecessary idling of school buses wastes fuel. One-half gallon of fuel is consumed every hour that a school bus idles its main engine. When considering the effects of idling on large school bus fleets, tens of thousands of dollars can be saved every year by reducing the average idle times of school buses in the fleet. The data in the chart below assumes that the school year is 180 days, idling consumes one-half gallon of fuel per hour, and diesel fuel costs $2.50 per gallon.

fuel savings
(Data based on 2009 information.)

  • Reducing idling 30 minutes per day yields $112.50 per year in fuel savings.
  • One hour of idling reduced per day yields $225 per year in fuel savings.

School Bus Emission Standards
The U.S. Environmental Protection Agency certifies engines that are used in vehicles, including school buses, across the country.  Every four years the emission standards for engines have been tightened to protect air quality. The newer the school bus, the cleaner the emissions are from the engine. School buses manufactured in 2007 and later emit approximately 90 percent fewer emissions than school buses that were manufactured prior to 1991.  School buses manufactured in 2010 and later will reduce 2007 emission levels by approximately 50 percent. The chart below shows the year that school buses that are currently in use were manufactured statewide.

Health Effects

Diesel emissions from school buses greatly contribute to the formation of ground-level ozone, and the ambient levels of fine particulate matter and air toxics. Ozone is also a primary pollutant of concern in Missouri. Unnecessary idling on school property exposes students to harmful diesel emissions. When idling, the amount of particulate matter emitted increases, because fuel is not fully combusted at the low RPM speeds associated with an idling engine. When pollution from diesel emissions combines in the presence of heat and sunlight, ground-level ozone, commonly known as smog, is created.

Ground-level ozone is an irritant that damages lung tissue, aggravates heart and respiratory disease and can even cause problems for healthy individuals who spend a lot of time outdoors. Ozone nonattainment areas must continue to take actions to prevent the formation of ground-level ozone. Control devices, such as diesel retrofitting and idling-reduction, are an important part of protecting air quality. Controlling harmful emissions and making air conscious decisions are necessary in order to protect public health and prevent the formation of ground-level ozone.

Adverse Health Effects Associated With Exposure to Diesel Emissions

For More Information 

Contact Mark Leath with the department's Air Pollution Control Program at the address below. Inquiries can also be made by calling 573-751-4817.

Air Quality Planning Section
Missouri Department of Natural Resources
Air Pollution Control Program
P.O. Box 176
Jefferson City, MO 65102-0176