The Clean Air Act (CAA) as amended in 1970 launched an ambitious national campaign to maintain healthy air quality by controlling air pollution. The 1990 amendments to the CAA renewed and intensified national efforts to reduce air pollution in the United States. These amendments presented a monumental challenge for regulatory officials, regulating industries, and others involved in this environmental control undertaking. The primary purposes of the actions mandated by the CAA were to improve public health, preserve property, and benefit the environment.

The CAA spells out the different roles of the federal and state governments. In general, the federal government develops the regulations and the states carry them out.

The CAA addresses interstate movement of air pollution, international air pollution, permits, enforcement, deadlines, and public participation. The CAA identifies air pollutants and sets primary and secondary standards for each. The primary standard protects human health, and the secondary standard is based on potential environmental and property damage. An area that meets or exceeds the primary standard is called an attainment area; an area that does not meet the primary standard is called a non-attainment area. An estimated 90 million Americans live in non-attainment areas.

The main or "criteria" air pollutants covered by the CAA are ozone, sulfur dioxide (SO₂), particulate matter, lead, nitrogen oxides (NO_x), and carbon monoxide (CO). The CAA includes specific limits, timelines, and procedures to reduce these criteria pollutants. The CAA also regulates what are called "hazardous air pollutants" (HAPs). HAPs are released by chemical plants, dry cleaners, printing plants, and motor vehicles. They can cause serious health and environmental effects.

The CAA includes specific goals for reducing emissions from all mobile sources. The comprehensive approach to reduce pollution from mobile sources includes requiring cleaner fuels; manufacturing cleaner cars, trucks, and buses; establishing inspection and maintenance (I/M) programs; and developing regulations for off-road vehicles and equipment.

SO₂ and NO_x, which are emitted by industrial furnaces and boilers, are regulated by the CAA under a comprehensive permit program. (SO₂ and NO_x contribute to acid rain.) The act protects stratospheric ozone by restricting the use of chlorofluorocarbons (CFCs) and regulating the use of volatile organic compounds (VOCs) in products.

Air pollution is the contamination of air by the discharge of harmful substances. Air pollution can cause health problems, including burning eyes and nose, itchy irritated throat, and difficulty breathing. Some contaminants found in polluted air (e.g., benzene, carbon dioxide, carbon monoxide, lead, nitrogen oxide, particulate matter, and sulfur dioxide) can cause cancer, birth defects, brain and nerve damage, and long-term injury to the lungs and breathing passages. Above certain concentrations and durations, air pollutants can be extremely dangerous and can cause severe injury or death.

Air pollution can also damage the environment and property. Plants and animals and their habitats can be harmed by air pollution. Air pollution has thinned the protective ozone layer above Earth. It can damage buildings, monuments, statues, and other structures. Air pollution can also result in haze, which reduces visibility and can sometimes interfere with aviation.

Carbon Monoxide (CO) is an odorless, colorless gas. After being inhaled, CO molecules can enter the bloodstream where they inhibit the delivery of oxygen throughout the body. Low concentrations can cause dizziness, headaches, and fatigue. High concentrations can be fatal. CO is produced by the incomplete burning of carbon-based fuels, including gasoline, oil, and wood. It is also produced from incomplete combustion of natural and synthetic products, such as cigarette smoke. It can build up in high concentrations in enclosed areas such as garages, poorly ventilated tunnels, and even along roadsides in heavy traffic.

Chlorofluorocarbons (CFCs) are chemicals used in industry, refrigeration and air conditioning systems, and consumer products. When released into the air, CFCs rise into the stratosphere. In the stratosphere, CFCs react with other chemicals and reduce the stratospheric ozone layer, which protects Earth's surface from the sun. Reducing CFC emissions and eliminating the production and use of ozone-destroying chemicals is very important to protecting Earth's stratosphere.

Hazardous Air Pollutants (HAPS) are chemicals that cause serious health and environmental effects. Health effects include cancer, birth defects, nervous system problems, and death due to massive accidental releases, such as occurred at a pesticide plant in Bhopal, India, in the mid-1980's. HAPs are released by sources such as chemical plants, dry cleaners, printing plants, and motor vehicles (e.g., cars, trucks, buses, and planes).

Lead is a highly toxic metal that produces a range of adverse health effects, particularly in young children. Lead can cause nervous system damage and learning behavior problems. Lead can also harm wildlife. Lead has been phased out of gasoline, which has reduced air contamination by lead considerably. However, lead can still be inhaled or ingested from other sources. These sources of lead include paint (both house and cars), smelters, manufacture of lead batteries, fishing lures, certain parts of bullets, some ceramic ware, water pipes, and fixtures.

Nitrogen Oxides (NO_x) are major contributors to ozone (smog) and acid rain. NO_x reacts with volatile organic compounds (VOCs) to form smog. In high doses, smog can harm humans by causing breathing difficulty for asthmatics, coughs in children, and general illness of the respiratory system. NO_x in combination with VOCs and in the presence of heat and sunlight form ground-level ozone, which can cause lung damage, chest pain, coughing, nausea, throat irritation, and congestion. Acid rain can harm vegetation and can run into lakes and rivers, which changes the chemistry of the water, making it potentially uninhabitable for all but acid-tolerant bacteria. NO_x are produced from burning fuels, including gasoline and coal.

Ozone (O₃) is a gas that consists of three oxygen atoms. Ozone forms naturally and is beneficial in the stratosphere (a layer of atmosphere high above Earth) where it filters harmful ultraviolet (UV) rays. However, ozone that is close to the ground (called ground-level ozone) can irritate the respiratory tract, cause chest pain and persistent cough, affect the ability to take a deep breath, and an increase susceptibility to lung infection. Ozone can also damage trees and plants and reduce visibility. Motor vehicles and industries are major sources of ground-level ozone. Ground-level ozone comes from the oxidation (breakdown) of VOCs found in solvents. It is also a product of reactions between chemicals produced by burning coal, gasoline, and other fuels and chemicals found in paints and hair sprays. Oxidation occurs readily during hot weather.

Particulate Matter (PM) includes fine solids suspended in the air in the form of smoke, dust, and vapors, which can remain suspended for extended periods. In addition to reducing visibility and soiling clothing, microscopic particles from the air can be breathed in and lodged in lung tissue, causing increased respiratory disease and lung damage. Particulates are also the main source of haze, which reduces visibility. Particulates are produced by many sources, including cars, trucks, and buses burning diesel fuels and other fossil fuels; the preparation and application of fertilizers and pesticides; road construction; industrial processes, such as steel making; mining; agricultural burning; and the operation of fireplaces and woodstoves. PM₁₀ is particulate matter smaller than 10 microns.

Sulfur Dioxide (SO₂) is an odorless gas at low concentrations, but at high concentrations can have a very strong smell. SO₂ is produced by burning coal, most notably in power plants. Some industrial processes, such as paper production and metal smelting, produce SO₂. Like NO_2, SO₂ is a major contributor to smog and acid rain. It can harm vegetation and metals and can cause lung problems, including breathing problems and permanent lung damage.

Volatile Organic Compounds (VOCs), like all organic compounds, contain carbon. Organic chemicals are the basic chemicals found in all living things and all products derived from living things. Many organic compounds that we use do not occur in nature, but are synthesized by chemists in laboratories. Volatile chemicals produce vapors easily at room temperature. VOCs include gasoline; industrial chemicals, such as benzene; solvents, such as toluene and xylene; and perchloroethylene (the principal dry cleaning solvent). VOCs are released from burning fuel, such as gasoline, wood, coal, or natural gas, and from solvents, paints, glues, and other products used at home or work. Vehicle emissions are an important source of VOCs. Many VOCs are also HAPs.

While laws and regulations go a long way toward ensuring cleaner air, individuals like you and your students can also contribute to making the air cleaner by reducing your own contribution from mobile sources (cars, lawn mowers, snowmobiles, etc.). This module focuses on vehicles and vehicle maintenance. Making informed and responsible choices, anyone can help to achieve cleaner air.

Since vehicles contribute to air pollution by emitting CO, NO_x, O₃, VOCs, HAPs, CFCs, and particulate matter, each driver who makes informed changes in their personal driving habits can contribute to the reduction of air pollution.

Congress enacted the Clean Air Act Amendments (CAAA) of 1990 to ensure clean air for all Americans. Under this law, the U.S. Environmental Protection Agency (EPA) sets limits on how much of specific pollutants can be in the air anywhere in the United States. These limits are known as the National Ambient Air Quality Standards (NAAQS). The standards help to ensure that people throughout the country have the same basic health and environmental protections. However, many U.S. cities are currently in violation of NAAQS. The primary emissions sources include on-road motor vehicles such as cars and buses; major and minor industries; and off-road motor vehicles such as construction equipment, boats, and planes. The CAAA set specific targets to reduce emissions from motor vehicles.

Motor vehicle emission control devices have dramatically reduced pollutant emissions per vehicle during the past 20 years. But the number of cars and trucks on the road, and the number of miles they are driven, have doubled. Vehicles are now driven more than a trillion miles each year in the United States. This growth in vehicle travel is offsetting the progress achieved through improved vehicle emission controls. Cars and trucks release millions of tons of pollutants into the air each year.

Motor vehicles generate three major pollutants: hydrocarbons, nitrogen oxides (NO_x), and carbon monoxide (CO). Hydrocarbons react with NO_x in the presence of sunlight to form ground-level ozone (smog). NO_x contribute to the formation of acid rain, although sulfur dioxide (SO₂) is the primary contributor. Acid rain increases the level of pollutants in lakes, rivers, bays, and other waterways. CO, a colorless, odorless gas, can impair mental functions and visual perception and is deadly in high concentrations. Motor vehicles also emit large quantities of carbon dioxide (CO₂), which has the potential to trap Earth's heat and contribute to global warming.

According to the EPA, two-thirds of CO emissions and nearly half the ozone-forming emissions come from mobile sources, such as motor vehicles. Typically, the older the car, the more pollution it emits. The EPA has found that 30 percent of five-year-old cars emit far more than they were designed to emit, contributing to air pollution more than the other 70 percent of vehicles of a similar age. Fifty-five percent of seven-year-old cars are "gross emitters." Overall, 10 to 30 percent of the vehicles on the road create the majority of the pollution from cars and trucks.

Mobile Source Contribution to Air Pollutant Inventories — 1995

Ozone is a colorless gas that consists of three oxygen atoms. Ground-level ozone is one of the main components of smog.

There are two types of ozone: stratospheric ozone (in the upper atmosphere) and tropospheric (ground-level) ozone. Stratospheric ozone is known as the ozone layer, and it protects our health by shielding us from the sun's damaging ultraviolet rays. However, at ground level, tropospheric ozone is a pollutant with highly toxic effects. It is harmful to human health, the environment, crops, and a wide range of natural and artificial materials.

Motor vehicles and industries are major sources of pollutants that cause ground-level ozone. Ground-level ozone (smog) is formed by the interaction of hydrocarbons (unburned or evaporated gasoline) and nitrogen oxides (NO_x) in the presence of sunlight. Smog also comes from the oxidation (breakdown) of volatile organic compounds (VOCs) found in solvents and is a product of reactions between chemicals produced by burning coal, gasoline, and other fuels and the chemicals found in products such as paints and hair sprays. Oxidation occurs readily in the presence of sunlight.

Ozone that is close to the ground can cause headaches, coughing, impaired lung function, and eye, nose, and throat irritation. Asthmatics and children are at greatest risk. Ozone can also worsen the effects of bronchitis, heart disease, and emphysema. The chance of experiencing adverse health effects from elevated ozone levels increases during heavy exercise or outdoor activity.

Many cities with high levels of ground-level ozone have established programs to raise awareness about days with particularly high ozone levels (sometimes called Ozone Action Days) and to encourage local residents to take action to reduce emissions and protect themselves. These voluntary initiatives are put into effect by cooperative efforts between government and environmental and business organizations to reduce ground-level ozone. Ozone Action Days occur most often on hot days — above 90^o Fahrenheit — with little or no wind blowing. Predictions for Ozone Action Days are announced on television and radio in advance to inform the public of responsible actions they can take to reduce air pollution. The warnings also inform the general public that the air quality is so poor it could affect asthmatics and cause other respiratory problems and to be careful in their outdoor activity.

Vehicle Maintenance, How to Find Your Way Under the Hood and Around the Car, (send a self-addressed stamped envelope), Car Care Council, 42 Park Drive, Port Clinton, OH 43452.

The Clean Air Act (CAA) addresses interstate movement of air pollution, international air pollution, permits, enforcement, deadlines, and public participation. The CAA sets primary and secondary standards for each specific air pollutant. The primary standard protects human health, and the secondary standard is based on potential environmental and property damage. The main or "criteria" pollutants covered by the CAA are ozone, sulfur dioxide (SO₂), particulate matter, lead, nitrogen oxide (NO_x), and carbon monoxide (CO). The comprehensive approach to reduce pollution from mobile sources includes promoting cleaner cars, trucks, and buses; establishing inspection and maintenance (I/M) programs; and developing regulations for off-road vehicles.

Automobiles can have many potentially negative effects on human health and the environment. The air we breathe, the water we drink, wildlife habitat, natural resources, and Earth's protective atmosphere are all affected by decisions we make about the vehicles we buy, how we drive them, how we refuel them, and how we maintain and repair them.

As more people become aware of the pollution automobiles create, and the simple actions and choices they can make to prevent this pollution, we can work together to improve air quality.

You cannot always see it, but the pollution from cars and trucks goes directly into the air we breathe. Emissions from cars and trucks can cause two of the worst air pollution problems: ground-level ozone (also known as smog) and carbon monoxide. Ground-level ozone/smog irritates the lungs and eyes and can lead to permanent lung damage. Carbon monoxide interferes with the blood's ability to carry oxygen to the brain, impairing mental functions and visual perception. It can be deadly in high concentrations. Motor vehicles also emit air toxins, which can cause serious health problems.

Each of us can do simple things to significantly reduce or prevent pollution from our cars.

The power to move a car typically comes from burning fuel in an internal combustion engine. Pollution from cars comes from by-products of this combustion process (exhaust) and evaporation of the fuel.

Gasoline and diesel fuels are mixtures of hydrocarbons, compounds that contain hydrogen and carbon atoms. In a perfect engine, oxygen in the air would convert all the hydrogen in the fuel to water and all the carbon in the fuel to carbon dioxide (CO₂). Nitrogen in the air would remain unaffected. But the combustion process is not perfect. As a result, automotive engines emit several types of pollutant by-products.