Mobile source air pollution includes any air pollution emitted by motor vehicles, airplanes, locomotives, and other engines and equipment that can be moved from one location to another. Many of these pollutants contribute to environmental degradation and have negative effects on human health. To prevent unnecessary damage to human health and the environment, environmental regulatory agencies such as the U.S. Environmental Protection Agency have established policies to minimize air pollution from mobile sources. Similar agencies exist at the state level. Due to the large number of mobile sources of air pollution, and their ability to move from one location to another, mobile sources are regulated differently from stationary sources, such as power plants. Instead of monitoring individual emitters, such as an individual vehicle, mobile sources are often regulated more broadly through design and fuel standards. Examples of this include corporate average fuel economy standards and laws that ban leaded gasoline in the United States. The increase in the number of motor vehicles driven in the U.S. has made efforts to limit mobile source pollution challenging. As a result, there have been a number of different regulatory instruments implemented to reach the desired emissions goals.
Broad classification
There are a number of different mobile sources of air pollution, some contributing more to pollution than others. As mentioned previously, mobile sources are regulated differently from stationary sources due to the large number of sources and their ability to move from one location to another. Different mobile sources operate differently and generate different emission types and levels. The E.P.A. differentiates between mobile sources by classifying them as either on-road vehicles or non-road vehicles. On-road vehicles and non-road vehicles are often subject to different regulations.
Road sources Cars Light Duty and Heavy Duty Trucks Buses Motorbikes
Non-road sources
Aircraft Motorboats (Diesel and Gasoline) Diesel locomotives Diesel multiple units Construction Equipment
Major regulated mobile source pollutants There are a number of different pollutants that are emitted by mobile sources. Some make up a large portion of the total air concentration for that particular pollutant while others do not make up as much of the total air concentration.
Carbon Monoxide: Carbon monoxide forms when carbon in fuel does not burn completely (incomplete combustion). The main source of carbon monoxide in air is vehicle emissions. As much as 95 percent of the carbon monoxide in typical U.S. cities comes from mobile sources, according to EPA studies. Carbon monoxide is harmful because it reduces oxygen delivery to the body's organs and tissues. It is most harmful to those who suffer from heart and respiratory disease. Carbon Dioxide: Carbon dioxide is one of the most prominent greenhouse gasses emitted by motor vehicles. In 2006, 23.6% of the total inventory of U.S. greenhouse gasses were derived from motor vehicles. The compound is generated as a byproduct of the combustion of any fuel source containing carbon. Nitrogen Oxides: Nitrogen oxides form when fuel burns at high temperatures, such as in motor vehicle engines. Mobile sources are responsible for more than half of all nitrogen oxide emissions in the United States. Both on-road and non-road mobile sources are major nitrogen oxide polluters. These problems include ozone and smog. Hydrocarbons: Hydrocarbons are a precursor to ground-level ozone, a serious air pollutant in cities across the United States. A key component of smog, ground-level ozone is formed by reactions involving hydrocarbons and nitrogen oxides in the presence of sunlight. Hydrocarbon emissions result from incomplete fuel combustion and from fuel evaporation. Ground-level ozone causes health problems such as difficulty breathing, lung damage, and reduced cardiovascular functioning. Particulate Matter: Atmospheric particulate matter or airborne 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 include asthma, difficult or painful breathing, and chronic bronchitis, especially in children and the elderly. Air Toxics: The EPA lists over 1100 individual compounds which are classified as air toxics. These compounds are emitted by mobile sources, mostly due to the chemical nature of the fuel source. These compounds are known or expected to cause serious physical damages including cancer, reproductive, and developmental side effects.
Laws and regulatory standards
U.S. enforcement agencies
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