Without healthy water for drinking, cooking, fishing, and farming, the human race would perish. Clean water is also necessary for recreational interests such as swimming, boating, and water skiing. Yet, when Congress began assessing national water quality during the early 1970s, it found that much of the country's groundwater and surface water was contaminated or severely compromised. Studies revealed that the nation's three primary sources of water pollution—industry, agriculture, and municipalities—had been regularly discharging harmful materials into water supplies throughout the country over a number of years.

These harmful materials included organic wastes, sediments, minerals, nutrients, thermal pollutants, toxic chemicals, and other hazardous substances. Organic wastes are produced by animals and humans, and include such things as fecal matter, crop debris, yard clippings, food wastes, rubber, plastic, wood, and disposable diapers. Such wastes require oxygen to decompose. When they are dumped into streams and lakes and begin to break down, they can deprive aquatic life of the oxygen it needs to survive.

Sediments may be deposited into lakes and streams through soil erosion caused by the clearing, excavating, grading, transporting, and filling of land. Minerals, such as iron, copper, chromium, platinum, nickel, zinc, and tin, can be discharged into streams and lakes as a result of various mining activities. Excessive levels of sediments and minerals in water can inhibit the penetration of sunlight, which reduces the production of photosynthetic organisms.

Nutrients, like phosphorus and nitrogen, support the growth of algae and other plants forming the lower levels of the food chain. However, excessive levels of nutrients from sources such as fertilizer can cause eutrophication, which is the overgrowth of aquatic vegetation. This overgrowth clouds the water and smothers some plants. Over time, excessive nutrient levels can accelerate the natural process by which bodies of water evolve into dry land.

Thermal pollution results from the release of heated water into lakes and streams. Most thermal pollution is generated by power plant cooling systems. Power plants use water to cool their reactors and turbines, and discharge it into lakes and tributaries after it has become heated. Higher water temperatures accelerate biological and chemical processes in rivers and streams, reducing the water's ability to retain dissolved oxygen. This can hasten the growth of algae and disrupt the reproduction of fish.

Toxic chemicals and other hazardous materials present the most imminent threat to water quality. The environmental protection agency (EPA) has identified 582 highly toxic chemicals, which are produced, manufactured, and stored in locations across the United States. Some chemical plants incinerate toxic waste, which produces dangerous by-products like furans and chlorinated dioxins, two of the most deadly carcinogens known to the human race. Other hazardous materials are produced or stored by households (motor oil, antifreeze, paints, and pesticides), dry cleaners (chlorinated solvents), farms (insecticides, fungicides, rodenticides, and herbicides), and gas stations and airports (fuel).

Water pollution regulation consists of a labyrinth of state and federal statutes, administrative rules, and common-law principles.

Federal statutory regulation of water pollution has been governed primarily by three pieces of legislation: the Refuse Act, the Federal Water Pollution Control Act, and the Clean Water Act. The Rivers and Harbors Appropriations Act of 1899, 33 U.S.C.A. § 401 et seq., commonly known as the Refuse Act, was the first major piece of federal legislation regulating water pollution. The Refuse Act set effluent standards for the discharge of pollutants into bodies of water. An effluent standard limits the amount of pollutant that can be released from a specific point or source, such as a smokestack or sewage pipe. The Refuse Act flatly prohibited pollution discharged from ship and shore installations.

The Refuse Act was followed by the Federal Water Pollution Control Act of 1948 (FWPCA), 33 U.S.C.A. § 1251 et seq. Instead of focusing on sources of pollution through effluent standards, the FWPCA created water quality standards, which prescribed the levels of pollutants permitted in a given body of water. Where the Refuse Act concentrated on deterring specific types of polluters, the FWPCA concentrated on reducing specific types of pollution.

Since 1972, federal regulation of water pollution has been primarily governed by the Clean Water Act (CWA) 33 U.S.C.A. § 1251 et seq., which overhauled FWCPA. The CWA forbids any person to discharge pollutants into U.S. waters unless the discharge conforms with certain provisions of the act. Among those provisions are several that call upon the EPA to promulgate effluent standards for particular categories of water polluters.

To implement these standards, the CWA requires each polluter to obtain a discharge permit issued by the EPA through the National Pollutant Discharge Elimination System (NPDES). Although the EPA closely monitors water pollution dischargers through the NPDES, primary responsibility for enforcement of the CWA rests with the states. Most states have also drafted permit systems similar to the NPDES. These systems are designed to protect local supplies of groundwater, surface water, and drinking water. Persons who violate either the federal or state permit system face civil fines, criminal penalties, and suspension of their discharge privileges.

The CWA also relies on modern technology to curb water pollution. It requires many polluters to implement the best practicable control technology, the best available technology economically achievable, or the best practicable waste treatment technology. The development of such technology for nontoxic polluters is based on a cost-benefit analysis in which the feasibility and expense of the technology is balanced against the expected benefits to the environment.

The CWA was amended in 1977 to address the nation's increasing concern about toxic pollutants. Pursuant to the 1977 amendments, the EPA increased the number of pollutants it deemed toxic from nine to 65, and set effluent limitations for the 21 industries that discharge them. These limitations are based on measures of the danger these pollutants pose to the public health rather than on cost-benefit analyses.

Many states have enacted their own water pollution legislation regulating the discharge of toxic and other pollutants into their streams and lakes.

The mining industry presents persistent water pollution problems for state and federal governments. It has polluted over a thousand miles of streams in Appalachia with acid drainage. In response, the affected state governments now require strip miners to obtain licenses before commencing activity. Many states also require miners to post bonds in an amount sufficient to repair potential damage to surrounding lakes and streams. Similarly, the federal government, under the Mineral Leasing Act, 30 U.S.C.A. § 201 et seq., requires each mining applicant to "submit a plan of construction,

operation and rehabilitation" for the affected area, that takes into account the need for "restoration, revegetation and curtailment of erosion."

The commercial timber industry also presents persistent water pollution problems. Tree harvesting, yarding (the collection of felled trees), and road building can all deposit soil sediments into watercourses, thereby reducing the water quality for aquatic life. State governments have offered similar responses to these problems. For instance, clear-cutting (the removal of substantially all the trees from a given area) has been prohibited by most states. Other states have created buffer zones around particularly vulnerable watercourses, and banned unusually harmful activities in certain areas. Enforcement of these water pollution measures has been frustrated by vaguely worded legislation and a scarcity of inspectors in several states.

State and federal water pollution statutes provide one avenue of legal recourse for those harmed by water pollution. The common-law doctrines of nuisance, trespass, negligence, strict liability, and riparian ownership provide alternative remedies.

Nuisances can be public or private. Private nuisances interfere with the rights and interests of private citizens, whereas public nuisances interfere with the common rights and interests of the people at large. Both types of nuisance must result from the "unreasonable" activities of a polluter, and inflict "substantial" harm on neighboring landowners. An injury that is minor or inconsequential will not result in liability under common-law nuisance. For example, dumping trace amounts of fertilizer into a stream abutting neighboring property will not amount to a public or private nuisance.

The oil and agricultural industries are frequently involved in state nuisance actions. Oil companies often run afoul of nuisance principles for improperly storing, transporting, and disposing of hazardous materials. Farmers represent a unique class of persons who fall prey to water pollution nuisances almost as often as they create them. Their abundant use of fungicides, herbicides, insecticides, and rodenticides makes them frequent creators of nuisances, and their use of streams, rivers, and groundwater for irrigation systems makes them frequent victims.

Nuisance actions deal primarily with continuing or repetitive injuries. Trespass actions provide relief even when an injury results from a single event. A polluter who spills oil, dumps chemicals, or otherwise contaminates a neighboring water supply on one occasion might avoid liability under nuisance law but not under the law of trespass. Trespass does not require proof of a substantial injury. However, only nominal damages will be awarded to a landowner whose water supply suffers little harm from the trespass of a polluter.

Trespass requires proof that a polluter intentionally or knowingly contaminated a particular course of water. Yet, water contamination often results from unintentional behavior, such as industrial accidents. In such instances, the polluter may be liable under common-law principles of negligence. Negligence occurs when a polluter fails to exercise the degree of care that would be reasonable under the circumstances. Thus, a landowner whose water supply was inadvertently contaminated might bring a successful lawsuit against the polluter for common-law negligence where a lawsuit for nuisance or trespass would fail.

Even when a polluter exercises the utmost diligence to prevent water contamination, an injured landowner may still have recourse under the doctrine of strict liability. Under this doctrine, polluters who engage in "abnormally dangerous" activities are held responsible for any water contamination that results. Courts consider six factors when determining whether a particular activity is abnormally dangerous: the probability that the activity will cause harm to another, the likelihood that the harm will be great, the ability to eliminate the risk by exercising reasonable care, the extent to which the activity is uncommon or unusual, the activity's appropriateness for a particular location, and the activity's value or danger to the community.

The doctrine of strict liability arose out of a national conflict between competing values during the industrial revolution. This conflict pitted those who believed it was necessary to create an environment that promoted commerce against those who believed it was necessary to preserve a healthy and clean environment. For many years, courts were reluctant to impose strict liability on U.S. businesses, out of concern over retarding industrial growth.

Since the early 1970s, courts have placed greater emphasis on preserving a healthy and clean environment. In Cities Service Co. v. State, 312 So. 2d 799 (Fla. App. 1975), the court explained that "though many hazardous activities … are socially desirable, it now seems reasonable that they pay their own way." Cities Service involved a situation in which a dam burst during a phosphate mining operation, releasing a billion gallons of phosphate slime into adjacent waterways, where fish and other aquatic life were killed. The court concluded that this mining activity was abnormally dangerous.

Some activities inherently create abnormally dangerous risks to abutting waterways. In such cases, courts do not employ a balancing test to determine whether an activity is abnormally dangerous. Instead, they consider these activities to be dangerous in and of themselves. The transportation and storage of high explosives and the operation of oil and gas wells are activities courts have held to create inherent risks of abnormally dangerous proportions.

The doctrine of riparian ownership forms the final prong of common-law recovery. A riparian proprietor is the owner of land abutting a stream of water, and has the right to divert the water for any useful purpose. Some courts define the term useful purpose broadly to include almost any purpose whatsoever, whereas other courts define it more narrowly to include only purposes that are reasonable or profitable.

In any event, downstream riparian proprietors are often placed at a disadvantage because the law protects upstream owners' initial use of the water. For example, an upstream proprietor may construct a dam to appropriate a reasonable amount of water without compensating a downstream proprietor. However, cases involving thermal pollution provide an exception to this rule. For example, downstream owners who use river water to make ice can seek injunctive relief to prevent upstream owners from engaging in any activities that raise the water temperature by even one degree Fahrenheit.

Andreen, William L. 2003. "The Evolution of Water Pollution Control in the United States—State, Local, and Federal Efforts, 1789–1972." Stanford Environmental Law Journal 22 (January).

Findley, Roger W., Daniel A. Farber, and Jody Freeman. 2003. Cases and Materials on Environmental Law. 6th ed. St. Paul, Minn.: West.

Hipfel, Steven J. 2001. "Enforcement of Nonpoint Source Water Pollution Control and Abatement Measures Applicable to Federal Facilities, Activities and Land Management Practices under Federal and State Law." Environmental Lawyer 8 (September).

Houck, Oliver A. 2002. The Clean Water Act TMDL Program: Law, Policy, and Implementation. 2d ed. Washington, D.C.: Environmental Law Institute.

Ryan, Mark A., ed. 2003. The Clean Water Act Handbook. 2d ed. Chicago: Section of Environment, Energy, and Resources, American Bar Association.

Air pollution is a phenomenon by which particles (solid or liquid) and gases contaminate the environment. Such contamination can result in health effects on the population, which might be either chronic (arising from long-term exposure), or acute (due to accidents). Other effects of pollution include damage to materials (e.g., the marble statues on the Parthenon are corroded as a result of air pollution in the city of Athens), agricultural damage (such as reduced crop yields and tree growth), impairment of visibility (tiny particles scatter light very efficiently), and even climate change (certain gases absorb energy emitted by the earth, leading to global warming).

Air pollution is certainly not a new phenomenon. Early references to it date back to the Middle Ages, when smoke from burning coal was already such a serious problem that in 1307 King Edward I banned its use in lime kilns in London. More recently, there have been major episodes of air pollution, such as the 1930 catastrophe in the Meuse Valley, Belgium, where SO2 and particulate matter, combined with a high relative humidity, caused sixty-three excess deaths in five days. In 1948 similar conditions in Donora, Pennsylvania, a small industrial city, caused twenty excess deaths in five days,

and in the early 1950s in London, England, two episodes of "killer fogs" claimed the lives of more than 6,000 people.

Not all pollutants are a result of human activity. Natural pollutants are those that are found in nature or are emitted from natural sources. For example, volcanic activity produces sulfur dioxide, and particulate pollution may derive from forest fires or windblown dust. Anthropogenic pollutants are those that are produced by humans or controlled processes. For example, sulfur dioxide is produced by fossil fuel combustion and particulate matter comes from diesel engines.

Air pollutants also are classified as primary or secondary. Primary pollutants are those that are emitted directly into the atmosphere from an identifiable source. Examples include carbon monoxide and sulfur dioxide. Secondary pollutants are those that are produced in the atmosphere by chemical and physical processes from primary pollutants and natural constituents. For example, ozone is produced by hydrocarbons and oxides of nitrogen (both of which may be produced by car emissions) and sunlight. See the table for a listing of estimated pollutant emissions in the United States in 1999.

The earliest programs to manage air quality in the United States date to the late 1880s; they attempted to regulate emissions from smokestacks using nuisance law municipal ordinances. Little progress was made in air pollution control during the first half of the twentieth century.

In the 1950s there was a shift away from nuisance law and municipal ordinances as the basis for managing air quality toward increased federal involvement. The Air Pollution Control Act of 1955 established a program for federally funded research grants in the area of air pollution, but the role of the federal government remained a limited one.

It was the Clean Air Act (CAA) of 1963 that further extended the federal government's powers in a significant way, allowing direct federal intervention to reduce interstate pollution.

The Clean Air Act Amendments (CAAA) of 1970 continued many of the programs established by prior legislation; however, several aspects of it represented major changes in strategy by expanding the role of the federal government. The 1970 CAAA defined two types of pollutants that were to be regulated: criteria and hazardous pollutants.

Criteria pollutants, regulated to achieve the attainment of the National Ambient Air Quality Standards (NAAQS), including primary standards for the protection of public health, ". . . the attainment and maintenance of which, . . . allowing an adequate margin of safety, are requisite to protect public health," and secondary standards for the protection of public welfare. The first six criteria pollutants were carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), total suspended particulate matter (TSP), hydrocarbons, and photochemical oxidants. Lead was added to the list in 1976. In 1979 the photochemical oxidants standard was replaced by one for ozone (O3), and in 1983 the hydrocarbons standard was dropped altogether. In 1987 TSP was changed to PM10, and in 1997 PM2.5 was added to the official list and the ozone standard revised.

National Emission Standards for Hazardous Air Pollutants (NESHAP) were established. Ahazardous air pollutant (HAP) was defined as one "to which no ambient air standard is applicable and that . . . causes, or contributes to, air pollution which may reasonably be anticipated to result in an increase in mortality or an increase in serious irreversible or incapacitating reversible illness." Examples include asbestos, mercury, benzene, arsenic, and radionuclides.

Even though the CAAA of 1970 and 1977 placed deadlines on the dates for compliance with the NAAQS, as of 1990 in many areas of the United States, a variety of criteria pollutants existed in concentrations greater than the standards allowed.

As a result, the CAAA of 1990 were passed. They contain eleven major divisions, referred to as titles, the most important of which are the following: Title I: Provisions for Attainment and Maintenance of NAAQS, Title II: Provisions Relating to Mobile Sources, Title III: Hazardous Air Pollutants, Title IV: Acid Deposition Control, Title V: Permits, and Title VI: Stratospheric Ozone Protection, Title VII: Provisions Relating to Enforcement, Title VIII: Miscellaneous Provisions, Title IX: Clean Air Research, Title X: Disadvantaged Business Concerns, and Title XI: Clean Air Employment Transition Assistance.

Air pollution and the problems it causes are not confined by any geopolitical boundaries. For example, the radioactive cloud resulting from the Chernobyl nuclear accident in 1986 traveled as far as Ireland. A United Nations report warns that haze produced by the burning of wood and fossil fuels is creating a two-mile-thick "Asian browncloud" that covers southeastern Asia and may be responsible for hundreds of thousands of respiratory deaths a year.

In the United States, federal pollution laws and regulations apply to all states, even though some states, such as California, have adopted more stringent standards. Similarly, in the European Union (EU) existing laws apply equally to all members. Countries such as Denmark and Germany, however, have elected to imposed stricter standards than those set by the EU.

International agreements aimed at reducing various pollutants have been signed by various countries. The Montreal Protocol was signed in 1987; its purpose is the reduction of chlorofluorocarbons (CFC), a class of compounds that destroy the stratospheric ozone layer. More recently, in 1997, a conference convened in Kyoto, Japan, to discuss ways of reducing carbon dioxide emissions and other greenhouse gases . The United States has not signed the Kyoto Protocol, arguing that such an agreement would impede its economic progress. It has, however, publicly stated its intention to embark on voluntary reductions of carbon dioxide and other greenhouse gases.

In general, air pollutants are divided into two classes: those for which a NAAQS may be set (in other words, the criteria pollutants), and those for which NAAQS are not appropriate (the HAPs). If the ambient concentration of the criteria pollutants is kept below the NAAQS value, then there will be no health damage due to air pollution. The HAP (mostly known or suspected carcinogens), on the other hand, are those that, even in low concentrations, cause significant damage.

Particulate Matter. Particulate matter (PM) is the term used to describe solid or liquid particles that are airborne and dispersed (i.e., scattered, separated). PM originates from a variety of anthropogenic sources, including diesel trucks, power plants, wood stoves, and industrial processes.

The original NAAQS for PM was set in 1970. In 1987, the total suspended particulate matter, TSP, was revised, and a PM10 (particulate matter with an aerodynamic diameter of 10 μm or less) standard was set. PM10, sometimes known as respirable particles, was felt to provide a better correlation of particle concentration with human health.

In 1997 the particulate matter standard was updated, to include the PM2.5 standard. These particles, known as "fine" particles, a significant fraction of which is secondary in nature, are especially detrimental to human health because they can penetrate deep into the lungs. Scientific studies show a link between PM2.5 (alone, or combined with other pollutants in the air) and a series of significant health effects, even death.

Fine particles are the major cause of reduced visibility in parts of the United States, including many of the national parks. Also, soils, plants, water, or materials are affected by PM. For example, particles containing nitrogen and sulfur that are deposited as acid rain on land or water bodies may alter the nutrient balance and acidity of those environments so that species composition and buffering capacity change. PM causes soiling and erosion damage to materials, including culturally important objects such as carved monuments and statues.

Carbon Monoxide. Carbon monoxide (CO) is a colorless, odorless, and at high levels a poisonous gas that is fairly unreactive. It is formed when carbon in fuels is not burned completely. The major source of CO is motor vehicle exhaust. In cities, as much as 95 percent of all CO emissions result from vehicular (automobile) emissions. Other sources of CO emissions include industrial processes, nontransportation-related fuel combustion, and natural sources such as wildfires.

CO has serious health effects on humans. An exposure to 50 ppm of CO for eight hours can cause reduced psychomotor performance, while CO is lethal to humans when concentrations exceed approximately 750 ppm. Hemoglobin, the part of blood that carries oxygen to body parts, has an affinity of CO that is about 240 times higher than that for oxygen, forming carboxyhemoglobin, COHb. Moreover, the release of oxygen by hemoglobin is reduced in the presence of COHb. However, the effects of CO poisoning are reversible once the CO source has been removed.

Sulfur Dioxide. Sulfur dioxide (SO2) is colorless, nonflammable, nonexplosive gas. Almost 90 percent of anthropogenic SO2 emissions are the result of fossil fuel combustion (mostly coal) in power plants and other stationary sources. A natural source of sulfur oxides is volcanic activities.

In general, exposure to SO2 irritates the human upper respiratory tract. The most serious air pollution episodes occurred when there was a synergistic effect of SO2 with PM and water vapor (fog). Because of this, it has proven difficult to isolate the effects of SO2 alone.

SO2 is one of the precursors of acid rain (the term used to describe the deposition of acidic substances from the atmosphere). Also, SO2 is the precursor of secondary fine sulfate particles, which in turn affect human health and reduce visibility. Prolonged exposure to SO2 and sulfate PM causes serious damage to materials such as marble, limestone, and mortar. The carbonates (e.g., limestone, CaCO3) in these materials are replaced by sulfates (e.g., gypsum, CaSO4) that are water-soluble and may be washed away easily by rain. This results in an eroded surface.

Nitrogen Dioxide. Nitrogen dioxide (NO2) is a reddish-brown gas. It is a lung irritant and is present in the highest concentrations among other oxides of nitrogen in ambient air. Nitric oxide (NO) and NO2 are collectively known as NOx.

Anthropogenic emissions of NOx come from high-temperature combustion processes, such as those occurring in automobiles and power plants. Natural sources of NO2 are lightning and various biological processes in soil. The oxides of nitrogen, much like sulfur dioxide, are precursors of acid rain and visibility-reducing fine nitrate particles.

Ozone. Ozone (O3) is a secondary pollutant and is formed in the atmosphere by the reaction of molecular oxygen, O2, and atomic oxygen, O, which comes from the photochemical decomposition of NO2. Volatile organic compounds or VOCs (e.g., what one smells when refuelling the car) must also be present if O3 is to accumulate in the atmosphere.

O3 occurs naturally in the stratosphere and provides a protective layer from the sun's ultraviolet rays high above the earth. However, at ground level, O3 is a lung and eye irritant and can cause asthma attacks, especially in young children or other susceptible individuals. O3, being a powerful oxidant, also attacks materials and has been found to cause reduced crop yields and stunt tree growth.

Lead. The major sources of lead (Pb) in the atmosphere in the United States are industrial processes from metals smelters. Thirty years ago, the major emissions of Pb resulted from cars burning leaded gasoline. In 2002 only aviation fuels contain relatively large amounts of Pb. The United States is currently working with the World Bank to eliminate the use of leaded gasoline in all countries still using such fuel.

Pb is a toxic metal and can accumulate in the blood, bones, and soft tissues. Even low exposure to Pb can cause mental retardation in children.

Hazardous Air Pollutants. Hazardous air pollutants (HAPs), commonly referred to as air toxics or toxic air pollutants, are pollutants known to cause or suspected of causing cancer or other serious human health effects or damage to the ecosystem.

EPA lists 188 HAPs and regulates sources emitting significant amounts of these identified pollutants. Examples of HAPs are heavy metals (e.g., mercury), volatile chemicals (e.g., benzene), combustion by-products (e.g., dioxins), and solvents (e.g., methylene chloride). HAPs are emitted from many sources, including large stationary industrial facilities (e.g., electric power plants), smaller-area sources (e.g., dry cleaners), mobile sources (e.g., cars), indoor sources (e.g., some building materials and cleaning solvents), and other sources (e.g., wildfires).

Potential human health effects of HAPs include headache, dizziness, nausea, birth defects, and cancer. Environmental effects of HAPs include toxicity to aquatic plants and animals as well as the accumulation of pollutants in the food chain.

Because of the potential serious harmful effects of the HAPs, even at very low concentrations, NAAQS are not appropriate. The EPA has set National Emission Standards for Hazardous Air Pollutants, NESHAP, for only eight of the HAP, including asbestos and vinyl chloride. The EPA regulates HAP by requiring each HAP emission source to meet Maximum Achievable Control Technology (MACT) standards. MACT is defined as "not less stringent than the emission control that is achieved in practice by the best controlled similar source."

In general, control of pollutants that are primary in nature, such as SO2, NO2, CO, and Pb, is easier than control of pollutants that are either entirely secondary (O3) or have a significant secondary component (PM2.5). Primary pollutants may be controlled at the source. For example, SO2 is controlled by the use of scrubbers, which are industrial devices that remove SO2 from the exhaust gases from power plants. SO2 emissions are also reduced by the use of low-sulfur coal or other fuels, such as natural gas, that contain lower amounts of sulfur. NO2 from industrial sources also may be minimized by scrubbing. NO2 from cars, as well as CO, are controlled by the use of catalytic converters, engine design modifications, and the use of cleaner burning grades of gasoline. Lead emissions have been reduced significantly since the introduction of lead-free gasoline.

Ozone and particulate matter are two of the most difficult pollutants to control. Reduction of oxides of nitrogen emissions, together with a reduction of VOC emissions is the primary control strategy for minimizing ozone concentrations. Because a large portion of PM2.5 is secondary in nature, its control is achieved by control of SO2, NO2, and VOC (which are the precursors of sulfates, nitrates, and carbon-containing particulates).

see also Acid Rain; Carbon Dioxide; Carbon Monoxide; Clean Air Act; Coal; Electric Power; Global Warming; Greenhouse Gases; Lead; Ozone; Petroleum; Toxic Release Inventory; Vehicular Pollution.

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