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tinyURL : hfxycwy | ID : 4391 Home   >   Air   >   Air Quality and Pollutants   >   Air pollutants   >   Mobile sources

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Mobile sources of air pollution

Mobile sources, both on-road vehicles and off-road vehicles and equipment, are significant contributors to air pollution in Minnesota. EPA’s 2008 emissions inventory shows that on- and off-road mobile sources account for approximately half of the total amount of NOX, SO2, PM2.5 and VOCs emitted in Minnesota, and contribute significantly to the formation of ground-level ozone. Transportation accounts for roughly 25% of greenhouse gas emissions in Minnesota.

There is growing concern about health impacts from air pollutants associated with traffic emissions. Studies have shown that people who live, work, or attend school near major roads have an increased incidence and severity of health problems that may be related to air pollution from roadway traffic. Despite significant reductions in tailpipe emissions over the past 40 years, particularly from standard passenger cars and trucks, we still have a long way to go in reducing mobile-source pollution because there are more cars driving more miles over the past decade.


Health impacts of vehicle emissions

Although vehicles are getting cleaner, exposure to their emissions still can have significant health effects for people living or working near high-traffic areas. Health effects include reduced lung function and impaired development in children, asthma, cardiovascular disease, low birth weight, pre-term newborns, and premature death.

Air-pollution health risks are generally higher in urban areas, where there is a high concentration of moving vehicles. Studies of traffic emissions note that areas 1000-1600 feet from highways and other major roads are most impacted by traffic-related pollution. An estimated 30% to 45% of people living in large North American cities live within such zones.

On-road gasoline vehicles

Tailpipe emissions from on-road gasoline vehicles have steadily declined since passage of the Clean Air Act in 1970. Tightening standards, voluntary agreements, and changes in fuel formulation reduced emissions from on-road gasoline vehicles up to 44% between 1970 and 2002. These reductions occurred despite increases in numbers of vehicles on the road and total number of vehicle miles traveled. This emission reduction trend among gasoline on-road vehicles is predicted to continue and could be accelerated by removing aging vehicles from our roads.

According to an EPA study of light-duty vehicles, 13% of vehicles are responsible for more than 50%  of the PM2.5 emissions from on-road vehicles13. These are older, dirtier vehicles, of which there is often a higher concentration in high-traffic zones. Identifying and repairing or retiring these high-polluting vehicles would have a positive impact on both local and regional air quality.

Diesel emissions

Emissions from diesel-powered vehicles and non-road diesel engines (especially heavy-duty vehicles and engines) do not have the same history of regulation as gasoline engines. Emissions standards were applied to on-road diesel vehicles and non-road engines decades later than on-road gasoline vehicles.

Annual Mobile Source U.S. NOX Emission Projections


In contrast to reductions from gasoline vehicles, NOX emissions from heavy-duty diesel trucks increased more than 90% between 1970 and 2002.Yet EPA anticipates that implementation of recent vehicle emissions standards and the inevitable fleet turnover with newer, cleaner vehicles (especially on-road gasoline and diesel vehicles) will significantly reduce total annual NOX emissions from mobile sources in the U.S.

Diesel PM2.5 Statewide Emissions 2008


Other pollutants show similar trends. Recent vehicle emissions standards for on-road and off-road diesel vehicles as well as gradual replacement with newer, cleaner vehicles will significantly reduce PM2.5 emissions from diesel mobile sources in Minnesota over the next few decades.

More work is needed

Emissions data suggest that the three most significant sources of diesel particle emissions are agricultural equipment, off-road construction and mining equipment, and on-road heavy-duty trucks. It is common for diesel engines to last 20 to 40 years. Many older vehicles and engines without emissions controls are still in use and turnover to a new fleet of clean equipment can be very slow. Acceleration of efforts to replace or retrofit emission controls on these vehicles or to remove them from roadways would have a significant effect on VOC, NOX and PM2.5 emissions, and would be especially beneficial for people living and working close to where this equipment is operated.


MPCA diesel initiatives

From 2006 the MPCA has used grants to directly fund and or administer the improvement of more than 2,800 diesel engines in Minnesota. By far, the vast majority of projects result in emission reductions on heavy duty engines.

MPCA efforts to reduce diesel engine emissions began with targeting school buses to better protect school children. Since 2006, more than 3,600 eligible school buses in Minnesota have been retrofitted with emission reduction devices. A final push to reach the last buses older than 2007 will end in 2013. This successful effort involved public and private partnerships to utilize and leverage direct state and federal funding from the MPCA.

MPCA concurrently worked to reduce idling emissions from 225 long-haul trucks and refrigeration trailers, retrofit 425 publicly owned heavy-duty trucks in the metro area, and implement emission-reducing technologies in a variety of heavy-duty diesel fleets and other diesel engines across Minnesota. 

MPCA’s recent non-school bus efforts focused on construction equipment and metro delivery trucks. Four MPCA DERA federal  diesel grant projects were completed in the summer of 2012 and 2013, resulting in the reduction of more than 3 tons of ground-level fine particle (PM2.5) pollution per year by:

  • Retrofitting 40 Metropolitan Airport Commission airport support vehicles
  • Replacing old engines in five 100-ton cranes operating on Twin Cities metro bridge projects
  • Funding the incremental cost of hybrid technology in the replacement of 11 new delivery trucks used for Twin Cities-area deliveries
  • Repowering a 1970 rock crusher engine with a Tier-3 engine near Rochester.

For diesel grant project stories and information, visit Grants/financial assistance for clean diesel projects.


Last modified on October 31, 2013 10:46

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