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Vehicles - Mobile Sources

Mobile sources include not only cars and trucks but also such "off-road" equipment as bulldozers, motorboats, locomotives, aircraft – even weed whackers. Emissions from these types of sources come not only from fuel combustion but also from fuel evaporating from containers and tanks during and after the fueling process. Many different fuels are used in mobile sources, and some burn cleaner than others. The type of mobile source and the type of fuel it uses will be major factors in how that source affects the environment.


Vehicles and Equipment

Highway vehicles include vehicles that are normally operated on roadways, including cars, trucks, buses and motorcycles. Off-road vehicles include a wide variety of equipment and engine types that are normally not operated on roadways. This includes vehicles and equipment used in construction, agriculture, aircraft, locomotive, marine, recreational, manufacturing and landscaping industries.

Diesel engines are used in applications such as construction, farming, locomotives and mining. Lawn and garden equipment such as lawnmowers, chainsaws, weed whackers and leaf blowers typically use gasoline-powered engines. Off-road vehicles also include dirt bikes, all terrain vehicles (ATVs) and snowmobiles.

EPA's Office of Transportation and Air Quality has helpful information about highway vehicles and off road equipment.


Mobile sources use many different fuels including gasoline, diesel and alternative. Gasoline comes from refined crude oil. Reformulated gasoline, known as RFG, is gasoline blended to burn more cleanly than conventional gasoline and to reduce smog-forming pollutants in the air we breathe. The Clean Air Act requires RFG to be used in cities that have challenges meeting federal air quality standards. Reformulated gasoline is currently used in 17 states and the District of Columbia. About 30% of gasoline sold in the U.S. is reformulated.

Diesel fuel also comes from refined crude oil. In 2007, all diesel-powered highway vehicles were required to use ultra-low sulfur diesel fuel with an average sulfur content of 15 parts per million (ppm) to help reduce emissions. Off-road equipment is also required to use ultra-low sulfur fuel.

Alternative fuels include biodiesel, ethanol, natural gas, propane, hydrogen and electricity. Visit EPA Renewable Fuel Standard Program for more information.

Regular unleaded gasoline contains 10% ethanol, while E15 gasoline contains 15% ethanol. For more information on E15 fuel, refer to the Fuel Quality Fact Sheets on the Wis. Department of Agriculture, Trade and Consumer Protection website.


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, visit California's South Coast Air Quality Management District.

How Mobile Source Emissions 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 (CO), which is produced by many mobile sources, 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 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 man-made VOC emissions and more than 60% of the man-made NOx emissions.

These very small particles are created in atmospheric reactions, resulting from emissions of NOx, VOC, sulfur dioxide (SO2) and ammonia (NH4). 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.

How Mobile Source Emissions Affect Human 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.

Consumer Information

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 greenhouse 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 Climate Change Research

Visibility Degradation

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

Vapor Recovery

Vapor recovery at gasoline dispensing facilities

Gasoline contains volatile organic compounds (VOCs) and hazardous air pollutants such as benzene and toluene. VOCs, along with oxides of nitrogen, react in the atmosphere to form ground-level ozone. State and federal laws require the control of gasoline vapors to prevent their escape into the atmosphere.

Stage I vapor recovery requirements

Stage I vapor recovery is a control strategy that captures gasoline vapors released when a tank truck delivers gasoline to a storage tank at a gasoline dispensing facility. As the tank truck fills the gasoline storage tank, the vapors present in the tank are returned to the truck, rather than released to the ambient air. The vapors are then brought back to the terminal where they are processed and turned back into liquid gasoline.

Stage I vapor recovery systems are required at gasoline dispensing facilities located in Brown, Calumet, Dane, Dodge, Door, Fond du Lac, Jefferson, Kenosha, Kewaunee, Manitowoc, Milwaukee, Outagamie, Ozaukee, Racine, Rock, Sheboygan, Walworth, Washington, Waukesha and Winnebago counties.

Annual certification of state 1 vapor control (pressure/vacuum) for gasoline tank trucks

State and federal regulations require gasoline tank trucks to have vapor collection equipment if the trucks deliver to a gasoline dispensing facility equipped with a Stage 1 vapor recovery system. These trucks must annually test their vapor collection equipment to verify vapor tightness and report those results to DNR to obtain the tank truck’s certification sticker. For more information on these testing requirements, refer to:

Notice: To ensure proper functionality, always download Air Management Program PDF forms to the computer before opening and entering information. To download, right click on the document link, choose "Save link as", and save the file to a location on the computer. Open the downloaded file using Adobe Reader. For more information, visit the PDF help page.

The DNR's Annual Pressure/Vacuum Certification for Gasoline Tank Trucks (Form 4500-197) can be used to demonstrate compliance with this testing requirement. Use of this form is voluntary. Test results can be submitted using another format, as long as all required information is included.

Stage II vapor recovery requirements

Stage II vapor recovery systems were required in Kenosha, Kewaunee, Manitowoc, Milwaukee, Ozaukee, Racine, Sheboygan, Washington and Waukesha counties. However, facilities in these counties may voluntarily remove or decommission their Stage II systems.

Stage II vapor recovery captures gasoline vapors when a vehicle is being fueled at the pump. The vapors are returned through the pump hose to the petroleum storage tank instead of being released into the air. However, newer vehicles are equipped with their own vapor recovery systems, called onboard refueling vapor recovery or ORVR. In 2012, the U.S. Environmental Protection Agency determined that ORVR reached widespread use, and that continued use of Stage II systems is redundant. For this reason, Stage II systems are no longer required.

For more information about changes to Stage II vapor recovery requirements in Wisconsin, refer to the following factsheets:

For more information about regulations affecting gasoline dispensing facilities, visit the department's Small Business Environmental Assistance Program resources for gas stations. The program's compliance calendar for gasoline dispensing facilities contains factsheets summarizing vapor recovery requirements and other relevant regulations.

Related Wisconsin Rules

Related Information

Voluntary Reductions

Voluntary Reductions

Several voluntary programs are in place to reduce emissions from cars, trucks and other motor vehicles.

Wisconsin Clean Diesel Grant Program
The DNR has established the Wisconsin Clean Diesel Grant Program to help reduce diesel emissions from both public and private vehicle fleets across the state.

Midwest Clean Diesel Initiative (MCDI)
This initiative is a public-private partnership to voluntarily reduce diesel emissions prior to, or in addition to mandatory deadlines. The goal of MCDI is to impact 1 million diesel engines by 2010, through operational changes, technological improvements and use of cleaner fuels.

Congestion Mitigation and Air Quality (CMAQ)
CMAQ is a federal funded program for transportation projects that improve air quality in counties that are either air quality non-attainment or maintenance areas for federal air standards. The program seeks projects that improve air quality including enhancing public transit and other alternative transportation, technologies that improve traffic flow and vehicle emissions.

In addition, individual actions can help improve air quality. Actions taken by individuals may seem small, but when taken in totality, they add up to cleaner air. Taking mass transit or carpooling, even if it is just once or twice a week, can reduce traffic congestion, pollution and save money! It costs roughly between 44 cents and 62 cents per mile (depending on car size and type) to own and operate a vehicle. Biking and walking instead of driving are zero-emission ways to travel that can help you and the air stay healthy.

  • Eco-driving is a fun, easy and inexpensive way to reduce mobile emissions, and anyone can do it! Through eco-driving drivers of any vehicle learn how to use their vehicles efficiently and safely to reduce vehicle emissions and be a safe driver. Check out this guide to Vehicle Care for Clean Air to learn more!
  • Fleets in Southeast region have succeeded in saving fuel and reducing emissions while eco-driving through a federal grant. Two fleets trained staff how to eco-drive and saw results immediately! Email DNR Air Education for the curriculum and teach your drivers how to eco-drive.

Other Requirements

Other Regulatory Requirements

Regulations for Emissions from Vehicles and Engines
Read about EPA regulations related to vehicle and engine emission standards.

Wisconsin DMV Vehicle Emissions Tests
The purpose of motor vehicle inspection and maintenance is to insure that existing vehicles are maintained and emissions are minimized as the vehicle ages. There are 7 counties in Wisconsin that are required to have motor vehicle inspection and maintenance programs: Kenosha, Milwaukee, Ozaukee, Racine, Sheboygan, Washington and Waukesha counties.

Off-Road Vehicles and Equipment
As with highway vehicles, the EPA sets emissions standards for exhaust and fuel management systems on off-road vehicles and equipment. In general, the emission standards have lagged behind the level control for highway vehicles simply due to the large range of engines and engine applications for off-road equipment.

Reformulated Gasoline
Reformulated gasoline (RFG) is required by the Federal Clean Air Act in certain areas, including a six-county area in Southeastern Wisconsin. The fuel is especially formulated to reduce volatile organic compound emissions (VOC), emissions of nitrogen oxide compounds (NOx) and certain toxic compounds such as benzene.

Renewable Fuels
Congress created the renewable fuel standard (RFS) program to reduce greenhouse gas emissions and expand the nation's renewable fuels sector while reducing reliance on imported oil. This program was authorized under the Energy Policy Act of 2005 and expanded under the Energy Independence and Security Act of 2007.

Transportation Conformity
Conformity is a Clean Air Act requirement that serves as a bridge to connect air quality and transportation planning activities and is jointly administrated by the U.S. EPA and the U.S. Department of Transportation. The conformity process ensures that federal funding and approval are given to highway and transit projects that are consistent or "conform" to air quality goals established by a state air quality implementation plan (SIP). Conformity means that transportation activities will not cause new air quality violations, worsen existing violations or delay timely attainment of the national ambient air quality standards.