Diesel 101

Diesel engines in trucks, buses, locomotives, marine vessels, and construction equipment emit a significant amount of pollution to the air in the eight northeast states. Emissions from diesel engines include particulate matter, nitrogen oxides, greenhouse gases, and air toxics. These emissions contribute to unhealthy levels of air pollution in the Northeast, where millions of residents are affected.

Pollutants of Concern

Nitrogen Oxides (NOx)
Nitrogen oxides form when fuel burns at high temperatures and cause a variety of health and environmental problems in locations far from their emissions source. These problems include ozone and smog, which are created in the atmosphere from nitrogen oxides, hydrocarbons, and sunlight. Ozone and smog can harm human health (causing lung damage and a variety of respiratory problems), damage the environment, and cause poor visibility. Nitrogen oxide emissions also contribute to the formation of particulate matter through chemical reactions in the atmosphere.

Particulate Matter (PM)
Particulate matter is the term for solid or liquid particles found in the air. Some particles are large or dark enough to be seen as soot or smoke, but fine particulate matter is tiny and is generally not visible to the naked eye. Fine particulate matter is a health concern because very fine particles can reach the deepest regions of the lungs. Health effects can include aggravated asthma, difficult or painful breathing, chronic bronchitis, and premature death in people with cardiopulmonary disease. Children and the elderly are especially at risk. Fine particulate matter associated with diesel exhaust is also thought to cause lung cancer and is therefore listed as a mobile source air toxic. Fine particulate matter can travel long distances on air currents and is also a major cause of haze, which reduces visibility, in cities and scenic areas throughout the United States.

Greenhouse Gases
The greenhouse gas carbon dioxide is a product of every kind of combustion, including burning fuel in engines and vehicles. Greenhouse gases are so named because they trap heat in the Earth’s atmosphere and tend to warm the planet, much as a gardener’s greenhouse keeps plants warm. Vehicle emissions are a major contributor to carbon dioxide in our air.

Air Toxics
Air toxics are those pollutants known or suspected to cause cancer or other serious health effects (such as reproductive problems or birth defects) or adverse environmental effects. Most air toxics originate from human activities, including mobile sources, while some air toxics are released from natural sources such as volcanic eruptions. Examples of toxic air pollutants include benzene and toluene.

Reducing Diesel Pollution

The good news is that recently established regulations and programs greatly reduce harmful emissions from diesel engines. EPA's Clean Diesel Trucks and Buses Rule and Nonroad Diesel Rule establish more stringent emissions standards for on-road diesel vehicles and diesel construction vehicles and equipment. Furthermore, new rulemaking will reduce emissions from the diesel locomotive and marine engines of the future. When the latest rules requiring the use of advanced emission control technology and clean diesel fuel with a sulfur content capped at 15 parts per million take effect, exhaust emissions will decrease by more than 90 percent. When fully implemented, these rules will achieve more than $100 billion in health benefits. However, these rules will apply only to newly manufactured engines. With diesel engines lasting up to 30 years and with approximately 11 million engines in use today, the full benefits of these rules will not be realized for decades.

Complementing these clean diesel rules is a range of federal, regional, and local programs that address emissions from diesel vehicles and equipment in use today. Please visit the sector pages for more information on these programs.