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.EPA - What are Mobile Sources?
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.EPA - On-road Vehicles and Engines 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.EPA - Mobile Source Emissions - Past, Present, and Future
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.EPA - Carbon Monoxide 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.EPA - Emission Facts: Average Carbon Dioxide Emissions Resulting from Gasoline and Diesel Fuel 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.EPA - Nitrogen Oxides 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.EPA - Hydrocarbons 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.EPA - Particulate Matter 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 Regulatory law Year of establishment Description Air Pollution Control Act 1955 First federal air pollution legislation Funded research for scope and sources of air pollution Clean Air Act 1963 Authorized the development of a national program to address air pollution related environmental problems Authorized research into techniques to minimize air pollution Motor Vehicle Air Pollution Control Act 1965 The first federal legislation designed to control emissions from automobiles Authorized the Department of Health, Education, and Welfare (subsequently separated into the Department of Education and the Department of Health and Human Services in 1979) to establish the first federally mandated light duty vehicle emission standards The act required a 72% reduction in hydrocarbon emissions, a 56% reduction in carbon monoxide emissions, and a complete elimination of crankcase hydrocarbon emissions for all light duty vehicles produced after 1968, using a 1963 base year. Air Quality Act 1967 Authorized enforcement procedures for air pollution problems involving interstate transport of pollutants Authorized expanded research activities Clean Air Act Extension 1970 Authorized the establishment of National Ambient Air Quality Standards Established requirements for State Implementation Plans to achieve the National Ambient Air Quality Standards Authorized the establishment of New Source Performance Standards for new and modified stationary sources Authorized the establishment of National Emissions Standards for Hazardous Air Pollutants Increased enforcement authority Authorized requirements for control of motor vehicle emissions Clean Air Act Amendments 1977 Authorized provisions related to the Prevention of Significant Deterioration Authorized provisions relating to areas which are non-attainment with respect to the National Ambient Air Quality Standards Clean Air Act Amendments 1990 Authorized programs for Acid Deposition Control Authorized a program to control 189 toxic pollutants, including those previously regulated by the National Emissions Standards for Hazardous Air Pollutants Established permit program requirements Expanded and modified provisions concerning the attainment of National Ambient Air Quality Standards Expanded and modified enforcement authority Established a program to phase out the use of chemicals that deplete the ozone layer.
U.S. enforcement agencies
Federal agencies
Environmental Protection Agency: The Environmental Protection Agency's Office of Air and Radiation (OAR) develops national programs, policies, and regulations for controlling air pollution and radiation exposure. OAR is concerned with pollution prevention and energy efficiency, indoor and outdoor air quality, industrial air pollution, pollution from vehicles and engines, radon, acid rain, stratospheric ozone depletion, climate change, and radiation protection. Department of Energy: The Department of Energy's clean air compliance activities are overseen by its Office of Health, Safety, and Security. Department of Transportation Federal Aviation Administration: Practically all aviation emission sources are independently regulated through equipment specific regulations, standards and recommended practices, and operational guidelines, which are established by a variety of organizations. For example, on-road vehicles, which take passengers to and from the airport, meet stringent Federal tailpipe standards set by EPA. Stationary sources on the airport, like power boilers and refrigeration chillers, must meet independent state regulations. And FAA certification is required for essentially all aviation equipment and processes. For example there are more than 60 standards that apply to aircraft engine design, materials of construction, durability, instrumentation and control, and safety, among others. These are in addition to the Fuel Venting and Exhaust Emission Requirements for Turbine Engine Powered Airplanes (FAR Part 34), which guide compliance with EPA’s aircraft exhaust emission standards. The International Civil Aviation Organization (ICAO) is a United Nations intergovernmental body responsible for worldwide planning, implementation, and coordination of civil aviation. ICAO sets emission standards for jet engines. These are the basis of FAA’s aircraft engine performance certification standards, established through EPA regulations.
Federal Highway Administration: The FHWA, EPA, the Health Effects Institute, and others have funded and conducted research studies to try to more clearly define potential risks from mobile source air toxics emissions associated with highway projects. The FHWA policies and procedures for implementing NEPA is prescribed by regulation in 23 CFR § 771.
National Highway Traffic Safety Administration: NHTSA administers the CAFE program, and the Environmental Protection Agency (EPA) provides the fuel economy data. NHTSA sets fuel economy standards for cars and light trucks sold in the U.S. while EPA calculates the average fuel economy for each manufacturer.
State-level agencies EPA has ten regional offices, each of which is responsible for the execution of programs within several states and territories. California is the only state which has its own regulatory agency, the California Air Resources Board (CARB). The other states are allowed to follow CARB or federal regulations.
Enforcement mechanisms and policy instruments
Federal, state, and local governments utilize a wide range of policy instruments to control pollution from mobile sources. On the federal level, many different agencies are responsible for regulating, or at least creating policies to limit, pollution from mobile sources. This is necessary given the broad range of objects that are considered “mobile sources,” from aircraft and off-road vehicles, to locomotives and on-road vehicles. The Federal Aviation Administration, for example, establishes standards to limit emissions from aircraft, whereas the U.S. Department of Transportation and Environmental Protection Agency administer various aspects of on-road vehicle fuel economy regulations. On the state level, mandatory vehicle emissions-testing programs are often required as part of the annual motor-vehicle registration process.
Labeling policies