Basics of Mobile Sources

1. Vehicles and Equipment.

Highway vehicles include vehicles that are normally operated on roadways such as cars, trucks, buses and motorcycles. For more information, go to the Environmental Protection Agency’s (EPA) Office of Transportation Air Quality web page. [Exit DNR][http://www.epa.gov/otaq/hwy.htm]

• Off-road equipment and vehicles include a wide variety of equipment and engine types that are normally not operated on roadways. This equipment includes applications in construction, agricultural, aircrafts, locomotives, marine vessels, recreational vehicles, industry, and landscaping. Diesel engines are used in applications such as construction, farming, locomotives, and mining. Lawn and garden equipment such as lawn mowers, chainsaws, weed whackers and leaf blowers typically use gasoline powered engines. The off-road category also includes many types of recreational vehicles, such as dirt bikes, ATVs, and snowmobiles. For more information, go to the EPA’s off road equipment web page [exit DNR].

2. Fuels

There are many different fuels used by mobile source vehicles and equipment including gasoline, diesel, and alternative fuels. Additional information on fuels can be found at EPA’s Office of Transportation Air Quality web site [exit DNR]

• Gasoline comes from refining crude oil and is burned in engines that use a spark to ignite the mixture of gasoline fumes and air. Reformulated gasoline (known as "RFG") is gas blended to burn cleaner by reducing smog-forming toxic pollutants. The Clean Air Act requires that RFG be used in cities with the worst smog pollution to reduce harmful emissions that cause ground-level ozone.
• Diesel fuel also comes from refining crude oil. It is burned in engines that use compression of the air and fuel to ignite the mixture. In 2007, all diesel powered highway vehicles were required to use ultra-low sulfur diesel fuel with an average sulfur content of 15 ppm to help reduce emissions. Off-road equipment will also be required to use ultra-low sulfur fuel. This requirement will be phased in beginning in 2007 and completed in 2010.
  • New Requirements in Chapter NR 445 for Reducing Particulate Emissions from Stationary Diesel Engines [PDF 89KB]
• Alternative Fuels include biodiesel, ethanol, natural gas, propane, hydrogen, and electricity. For general information on alternative fuels visit EPA’s alternative fuels web page [exit DNR].
• Biodiesel is derived from a renewable resource such as vegetable oil or animal fat. Most biodiesel in the U.S. is made from soybean oil and is typically blended with petroleum based diesel to reduce emissions and replace a portion of the petroleum that is used in diesel fuel. For more information, visit EPA’s biodiesel website [exit DNR] or Wisconsin’s Power Initiative web site [exit DNR].
• Ethanol is an alcohol that is often mixed with gasoline and used as a motor fuel. Most of the ethanol in the U.S. comes from processing biomass such as corn, though research continues to explore using other sources such as switch grass. Most cars are able to burn a mixture of 90% gasoline and 10% ethanol without any problem. Flex-fueled vehicles are designed to burn up to 85% ethanol and 15% gasoline.
• Natural gas, which is mostly methane, can be used in both gasoline and diesel engines. Vehicles using natural gas as a fuel need significant modifications in order to use the fuel.
• Propane is a gas that comes from refining crude oil. It has been used as a substitute for gasoline for many years. Some off-road engines are designed to use propane such as forklifts. Using propane in highway vehicles usually requires some modifications of the vehicles in order to burn the gas.
• Hydrogen is the most abundant element in the universe. It is a combustible gas, but its application in motor vehicles will mostly be in fuel cells that generate electricity to power the vehicle. Fuel cell technology and storing hydrogen on the vehicle are challenges that face this emerging technology.
• Electricity has been used to power vehicles for more than 100 years. Batteries on the vehicle store electricity to power electric motors. Hybrid vehicles use a combination of the electric motors and a gasoline or diesel powered engine. Emerging fuel cell technology uses electricity to power a vehicle, but requires an underlying fuel source, such as hydrogen, to generate the electricity.

3. How mobile sources affect air pollution

The type and amount of emissions from specific mobile sources depends on multiple factors including the type of fuel being combusted and the age and efficiency of a vehicle. However, there are some general effects listed below.

Carbon Monoxide
Carbon Monoxide (CO) can cause serious health problems because it reduces the amount of oxygen reaching the body’s organs and tissues. More than 90% of the CO in the atmosphere results from incomplete combustion in mobile sources.

Ground Level Ozone
Ground level ozone is created by a reaction of volatile organic compounds (VOC) and nitrogen oxides (NOx) in the presence of heat and sunlight. Mobile sources are significant sources of these two principal precursor pollutants. In Wisconsin, mobile sources account for more than 40% of the manmade VOC emissions and more than 60% of the manmade NOx emissions.

Particulate Matter (PM2.5)
These very small particles are created in atmospheric reactions resulting from emissions of NOx, VOC, SO2 (sulfur dioxide) and ammonia. In Wisconsin, mobile sources account for more than 40% of the man-made VOC emissions and more than 60% of the man-made NOx emissions. Gasoline powered cars may be a significant source of ammonia. Some recent research indicates that ammonia emissions from these vehicles are significantly underestimated.

Toxics
There are many toxic chemicals emitted from mobile sources and their associated fueling systems. The pollutants that are of most concern are acrolein, benzene, 1-3 butadiene, formaldehyde, acetaldehyde, and diesel PM. A recent study in California indicates that about 90% of the risk of cancer from air pollutions is associated with diesel PM. For more information, go to California’s South Coast Air Quality Management District web site [exit DNR].

Visibility Degradation
Visibility degradation, or haze, results from tiny particles in the atmosphere that diffuse light. The same pollutants, NOx, VOC, SO2, and ammonia, which contribute to PM2.5, are also significant contributors to haze.

Climate Change
Mobile sources are significant sources of CO2 (carbon dioxide), methane, N2O (nitrous oxide) and HFCs (hydrofluorocarbons). All four compounds are principal contributors to green house gases and climate change, although, CO2 is by far the largest contributor. In Wisconsin, highway vehicles emit about 33 million tons of CO2 per year. Off-road equipment emit about 3 million tons of CO2 per year. For more information, visit EPA’s Climate Change Web Site [exit DNR].

4. How mobile source emissions affect your health

Mobile sources are implicated in creating adverse health effects from carbon monoxide, ground level ozone, and fine-particles. The health effects include premature death, aggravated asthma, immune system depression, cardio-pulmonary problems, and lost school and work days. Additionally, other toxic emissions from mobile sources are known to cause cancer along with creating respiratory problems. Find out more about the health effects of air pollutants by visiting these EPA web pages:

• EPA’s National Ambient Air Quality Standards [exit DNR]
• Mobile Source - Health Effects web pages [exit DNR]