OzoneOzone (O3) is a gas composed of three oxygen atoms. It is not usually emitted directly into the air, but at ground-level is created by a chemical reaction between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Ozone has the same chemical structure whether it occurs miles above the earth or at ground-level and can be "good" or "bad," depending on its location in the atmosphere.

In the earth's lower atmosphere, ground-level ozone is considered "bad." Motor vehicle exhaust and industrial emissions, gasoline vapors, and chemical solvents as well as natural sources emit NOx and VOC that help form ozone. Ground-level ozone is the primary constituent of smog. Sunlight and hot weather cause ground-level ozone to form in harmful concentrations in the air. As a result, it is known as a summertime air pollutant. Many urban are National Trends in Ozone Levels

Using a nationwide network of monitoring sites, EPA has developed ambient air quality trends for ozone. Trends are shown here for the 8-hour ozone standards. Under the Clean Air Act, EPA sets and reviews national air quality standards for ozone. Air quality monitors measure concentrations of ozone throughout the country. EPA, state, tribal and local agencies use that data to ensure that ozone is at levels that protect public health and the environment. Nationally, average ozone levels declined in the 1980's, leveled off in the 1990's, and showed a notable decline after 2002. For information on ozone standards, sources, health effects, and programs to reduce ozone, please see www.epa.gov/air/ozonepollution/.

as tend to have high levels of "bad" ozone, but even rural areas are also subject to increased ozone levels because wind carries ozone and pollutants that form it hundreds of miles away from their original sources.

"Good" ozone occurs naturally in the stratosphere approximately 10 to 30 miles above the earth's surface and forms a layer that protects life on earth from the sun's harmful rays. Learn more about how ozone can be beneficial up high in the stratosphere but harmful at ground level.

Basic InformationGround-level or "bad" ozone is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOC.

Breathing ozone, a primary component of smog, can trigger a variety of health problems including chest pain, coughing, throat irritation, and congestion. It can worsen bronchitis, emphysema, and asthma. Ground-level ozone also can reduce lung function and inflame the linings of the lungs. Repeated exposure may permanently scar lung tissue.

Ground-level ozone also damages vegetation and ecosystems. In the United States alone, ozone is responsible for an estimated $500 million in reduced crop production each year.

Under the Clean Air Act, EPA has set protective health-based standards for ozone in the air we breathe. EPA and others have instituted a variety of multi-faceted programs to meet these health-based standards. More about EPA ‘s ozone standards and regulatory actions.

Throughout the country, additional programs are being put into place to cut NOx and VOC emissions from vehicles, industrial facilities, and electric utilities. Programs are also aimed at reducing pollution by reformulating fuels and consumer/commercial products, such as paints and chemical solvents that contain VOC. Voluntary and innovative programs also encourage communities to adopt practices, such as carpooling, to reduce harmful emissions. More about EPA’s innovative programs to reduce air pollution.

Health

Breathing ozone can trigger a variety of health problems including chest pain, coughing, throat irritation, and congestion. It can worsen bronchitis, emphysema, and asthma. Ground-level ozone also can reduce lung function and inflame the linings of the lungs. Repeated exposure may permanently scar lung tissue.

The Clean Air Act requires EPA to set air quality standards to protect both public health and the public welfare (e.g. crops and vegetation). Ground-level ozone affects both.

Health Effects

People with lung disease, children, older adults, and people who are active can be affected when ozone levels are unhealthy. Numerous scientific studies have linked ground-level ozone exposure to a variety of problems, including:

airway irritation, coughing, and pain when taking a deep breath;

wheezing and breathing difficulties during exercise or outdoor activities;

inflammation, which is much like a sunburn on the skin;

aggravation of asthma and increased susceptibility to respiratory illnesses like pneumonia and bronchitis; and,

permanent lung damage with repeated exposures.

Using a nationwide network of monitoring sites, EPA has developed ambient air quality trends for ozone. Trends are shown here for the 8-hour ozone standards. Under the Clean Air Act, EPA sets and reviews national air quality standards for ozone. Air quality monitors measure concentrations of ozone throughout the country. EPA, state, tribal and local agencies use that data to ensure that ozone is at levels that protect public health and the environment. Nationally, average ozone levels declined in the 1980's, leveled off in the 1990's, and showed a notable decline after 2002. For information on ozone standards, sources, health effects, and programs to reduce ozone, please see www.epa.gov/air/ozonepollution/.

Particulate Matter

Particulate matter," also known as particle pollution or PM, is a complex mixture of extremely small particles and liquid droplets. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.

The size of particles is directly linked to their potential for causing health problems. EPA is concerned about particles that are 10 micrometers in diameter or smaller because those are the particles that generally pass through the throat and nose and enter the lungs. Once inhaled, these particles can affect the heart and lungs and cause serious health effects. EPA groups particle pollution into two categories:

"Inhalable coarse particles," such as those found near roadways and dusty industries, are larger than 2.5 micrometers and smaller than 10 micrometers in diameter.

"Fine particles," such as those found in smoke and haze, are 2.5 micrometers in diameter and smaller. These particles can be directly emitted from sources such as forest fires, or they can form when gases emitted from power plants, industries and automobiles react in the air.

Basic Information

Particle pollution (also called particulate matter or PM) is the term for a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Others are so small, they can only be detected using an electron microscope.

Particle pollution includes "inhalable coarse particles," with diameters larger than 2.5 micrometers and smaller than 10 micrometers and "fine particles," with diameters that are 2.5 micrometers and smaller. How small is 2.5 micrometers? Think about a single hair from your head. The average human hair is about 70 micrometers in diameter – making it 30 times larger than the largest fine particle.

These particles come in many sizes and shapes and can be made up of hundreds of different chemicals. Some particles, known as primary particles are emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks or fires. Others form in complicated reactions in the atmosphere of chemicals such as sulfur dioxides and nitrogen oxides that are emitted from power plants, industries and automobiles. These particles, known as secondary particles, make up most of the fine particle pollution in the country.

EPA regulates inhalable particles (fine and coarse). Particles larger than 10 micrometers (sand and large dust) are not regulated by EPA. More about EPA PM Standards and Regulatory Actions.

How Big is Particle Pollution?

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Health: Particle pollution contains microscopic solids or liquid droplets that are so small that they can get deep into the lungs and cause serious health problems. The size of particles is directly linked to their potential for causing health problems. Small particles less than 10 micrometers in diameter pose the greatest problems, because they can get deep into your lungs, and some may even get into your bloodstream. More information about health.

Visibility: Fine particles (PM2.5) are the major cause of reduced visibility (haze) in parts of the United States, including many of our treasured national parks and wilderness areas. More information about visibility.

Reducing particle pollution: EPA’s national and regional rules to reduce emissions of pollutants that form particle pollution will help state and local governments meet the Agency’s national air quality standards. More information about reducing particle pollution.

HealthThe size of particles is directly linked to their potential for causing health problems. Small particles less than10 micrometers in diameter pose the greatest problems, because they can get deep into your lungs, and some may even get into your bloodstream.

Exposure to such particles can affect both your lungs and your heart. Small particles of concern include "inhalable coarse particles" (such as those found near roadways and dusty industries), which are larger than 2.5 micrometers and smaller than 10 micrometers in diameter; and "fine particles" (such as those found in smoke and haze), which are 2.5 micrometers in diameter and smaller.

The Clean Air Act requires EPA to set air quality standards to protect both public health and the public welfare (e.g. crops and vegetation). Particle pollution affects both.

Health Effects

Particle pollution - especially fine particles - contains microscopic solids or liquid droplets that are so small that they can get deep into the lungs and cause serious health problems. Numerous scientific studies have linked particle pollution exposure to a variety of problems, including:

increased respiratory symptoms, such as irritation of the airways, coughing, or difficulty breathing, for example;

decreased lung function; aggravated asthma; development of chronic bronchitis; irregular heartbeat; nonfatal heart attacks; and premature death in people with heart or lung disease.

People with heart or lung diseases, children and older adults are the most likely to be affected by particle pollution exposure. However, even if you are healthy, you may experience temporary symptoms from exposure to elevated levels of particle pollution.

Environmental Effects

Visibility reductionFine particles (PM2.5) are the major cause of reduced visibility (haze) in parts of the United States, including many of our treasured national parks and wilderness areas. For more information about visibility, visit www.epa.gov/visibility.

Environmental damageParticles can be carried over long distances by wind and then settle on ground or water.  The effects of this settling include: making lakes and streams acidic; changing the nutrient balance in coastal waters and large river basins; depleting the nutrients in soil; damaging sensitive forests and farm crops; and affecting the diversity of ecosystems. More information about the effects of particle pollution and acid rain.

Aesthetic damageParticle pollution can stain and damage stone and other materials, including culturally important objects such as statues and monuments. More information about the effects of particle pollution and acid rain.

National Trends in Particulate Matter Levels

Using a nationwide network of monitoring sites, EPA has developed ambient air quality trends for particle pollution, also called Particulate Matter (PM). Trends from 1990-2009 are shown here for PM2.5 and PM10. Under the Clean Air Act, EPA sets and reviews national air quality standards for PM. Air quality monitors measure concentrations of PM throughout the country. EPA, state, tribal and local agencies use that data to ensure that PM in the air is at levels that protect public health and the environment. Nationally, average PM concentrations have decreased over the years. For information on PM standards, sources, health effects, and programs to reduce PM, please see www.epa.gov/air/particlepollution.

Carbon MonoxideCarbon monoxide (CO) is a colorless, odorless gas emitted from combustion processes.  Nationally and, particularly in urban areas, the majority of CO emissions to ambient air come from mobile sources.  CO can cause harmful health effects by reducing oxygen delivery to the body's organs (like the heart and brain) and tissues.  At extremely high levels, CO can cause death.

EPA first set air quality standards for CO in 1971.  For protection of both public health and welfare, EPA set a 8-hour primary standard at 9 parts per million (ppm) and a 1-hour primary standard at 35 ppm. 

In a review of the standards completed in 1985, EPA revoked the secondary standards (for public welfare) due to a lack of evidence of adverse effects on public welfare at or near ambient concentrations.

The last review of the CO NAAQS was completed in 1994 and the Agency chose not to revise the standards at that time.

HealthCO can cause harmful health effects by reducing oxygen delivery to the body's organs (like the heart and brain) and tissues.  At extremely high levels, CO can cause death.

Exposure to CO can reduce the oxygen-carrying capacity of the blood.  People with several types of heart disease already have a reduced capacity for pumping oxygenated blood to the heart, which can cause them to experience myocardial ischemia (reduced oxygen to the heart), often accompanied by chest pain (angina), when exercising or under increased stress.  For these people, short-term CO exposure further affects their body’s already compromised ability to respond to the increased oxygen demands of exercise or exertion.

National Trends in CO Levels

Using a nationwide network of monitoring sites, EPA has developed ambient air quality trends for carbon monoxide (CO). Trends from 1980-2008 and from 1990-2008 are shown here. Under the Clean Air Act, EPA sets and reviews national air quality standards for CO. Air quality monitors measure concentrations of CO throughout the country. EPA, state, tribal and local agencies use that data to ensure that CO remains at levels that protect public health and the environment. Nationally, average CO concentrations have decreased substantially over the years. For information on CO standards, sources, health effects, and programs to reduce CO, please see www.epa.gov/air/urbanair/co.

Nitrogen DioxideNitrogen dioxide (NO2) is one of a group of highly reactive gasses known as "oxides of nitrogen," or "nitrogen oxides (NOx)."   Other nitrogen oxides include nitrous acid and nitric acid. While EPA’s National Ambient Air Quality Standard covers this entire group of NOx, NO2 is the component of greatest interest and the indicator for the larger group of nitrogen oxides. NO2 forms quickly from emissions from cars, trucks and buses, power plants, and off-road equipment. In addition to contributing to the formation of ground-level ozone, and fine particle pollution, NO2 is linked with a number of adverse effects on the respiratory system.

EPA first set standards for NO2 in 1971, setting both a primary standard (to protect health) and a secondary standard (to protect the public welfare) at 0.053 parts per million (53 ppb), averaged annually.  The Agency has reviewed the standards twice since that time, but chose not to revise the standards at the conclusion of each review.  All areas in the U.S. meet the current (1971) NO2 standards.

HealthCurrent scientific evidence links short-term NO2 exposures, ranging from 30 minutes to 24 hours, with adverse respiratory effects including airway inflammation in healthy people and increased respiratory symptoms in people with asthma.

Also, studies show a connection between breathing elevated short-term NO2 concentrations, and increased visits to emergency departments and hospital admissions for respiratory issues, especially asthma.

NO2 concentrations in vehicles and near roadways are appreciably higher than those measured at monitors in the current network. In fact, in-vehicle concentrations can be 2-3 times higher than measured at nearby area-wide monitors. Near-roadway (within about 50 meters) concentrations of NO2 have been measured to be approximately 30 to 100% higher than concentrations away from roadways.

Individuals who spend time on or near major roadways can experience short-term NO2 exposures considerably higher than measured by the current network. Approximately 16% of U.S housing units are located within 300 ft of a major highway, railroad, or airport (approximately 48 million people). This population likely includes a higher proportion of non-white and economically-disadvantaged people.

NO2 exposure concentrations near roadways are of particular concern for susceptible individuals, including people with asthma asthmatics, children, and the elderly

The sum of nitric oxide (NO) and NO2 is commonly called nitrogen oxides or NOx. Other oxides of nitrogen including nitrous acid and nitric acid are part of the nitrogen oxide family. While EPA’s National Ambient Air Quality Standard (NAAQS) covers this entire family, NO2 is the component of greatest interest and the indicator for the larger group of nitrogen oxides.

NOx react with ammonia, moisture, and other compounds to form small particles. These small particles penetrate deeply into sensitive parts of the lungs and can cause or worsen respiratory disease, such as emphysema and bronchitis, and can aggravate existing heart disease, leading to increased hospital admissions and premature death.

Ozone is formed when NOx and volatile organic compounds react in the presence of heat and sunlight. Children, the elderly, people with lung diseases such as asthma, and people who work or exercise outside are at risk for adverse effects from ozone. These include reduction in lung function and increased respiratory symptoms as well as respiratory-related emergency department visits, hospital admissions, and possibly premature deaths.

Emissions that lead to the formation of NO2 generally also lead to the formation of other NOx. Emissions control measures leading to reductions in NO2 can generally be expected to reduce population exposures to all gaseous NOx. This may have the important co-benefit of reducing the formation of ozone and fine particles both of which pose significant public health threats.

National Trends in Nitrogen Dioxide Levels

Using a nationwide network of monitoring sites, EPA has developed ambient air quality trends for nitrogen dioxide (NO2). Trends from 1980-2009 and from 1990-2009 are shown here. Under the Clean Air Act, EPA sets and reviews national air quality standards for NO2. Air quality monitors measure concentrations of NO2 throughout the country. EPA, state, tribal and local agencies use that data to ensure that NO2 in the air is at levels that protect public health and the environment. Nationally, average NO2 concentrations have decreased substantially over the years. For information on NO2 standards, sources, health effects, and programs to reduce NO2, please see www.epa.gov/airquality/nitrogenoxides/.

Sulfur Dioxide

Sulfur dioxide (SO2) is one of a group of highly reactive gasses known as “oxides of sulfur.”  The largest sources of SO2 emissions are from fossil fuel combustion at power plants (73%) and other industrial facilities (20%).  Smaller sources of SO2 emissions include industrial processes such as extracting metal from ore, and the burning of high sulfur containing fuels by locomotives, large ships, and non-road equipment.  SO2 is linked with a number of adverse effects on the respiratory system.                                               EPA first set standards for SO2 in 1971.  EPA set a 24-hour primary standard at 140 ppb and an annual average standard at 30 ppb (to protect health).  EPA also set a 3-hour average secondary standard at 500 ppb (to protect the public welfare).

The last review of the SO2 NAAQS was completed in 1996 and the Agency chose not to revise the standards.  In the last review, EPA also considered, but did not set, a five minute NAAQS to protect asthmatics at elevated ventilation rates from bronchoconstriction and respiratory symptoms associated with 5-10 minute peaks of SO2.

HealthCurrent scientific evidence links short-term exposures to SO2, ranging from 5 minutes to 24 hours, with an array of adverse respiratory effects including bronchoconstriction and increased asthma symptoms. These effects are particularly important for asthmatics at elevated ventilation rates (e.g., while exercising or playing.)  

Studies also show a connection between short-term exposure and increased visits to emergency departments and hospital admissions for respiratory illnesses, particularly in at-risk populations including children, the elderly, and asthmatics.

EPA’s National Ambient Air Quality Standard for SO2 is designed to protect against exposure to the entire group of sulfur oxides (SOx).  SO2 is the component of greatest concern and is used as the indicator for the larger group of gaseous sulfur oxides (SOx).  Other gaseous sulfur oxides (e.g. SO3) are found in the atmosphere at concentrations much lower than SO2.      

Emissions that lead to high concentrations of SO2 generally also lead to the formation of other SOx.  Control measures that reduce SO2 can generally be expected to reduce people’s exposures to all gaseous SOx.  This may have the important co-benefit of reducing the formation of fine sulfate particles, which pose significant public health threats.

SOx can react with other compounds in the atmosphere to form small particles. These particles penetrate deeply into sensitive parts of the lungs and can cause or worsen respiratory disease, such as emphysema and bronchitis, and can aggravate existing heart disease, leading to increased hospital admissions and premature death.  EPA’s NAAQS for particulate matter (PM) are designed to provide protection against these health effects.

National Trends in Sulfur Dioxide Levels

Using a nationwide network of monitoring sites, EPA has developed ambient air quality trends for sulfur dioxide (SO2). Trends from 1980-2009 and from 1990-2009 are shown here. Under the Clean Air Act, EPA sets and reviews national air quality standards for SO2. Air quality monitors measure concentrations of SO2 throughout the country. EPA, state, tribal and local agencies use that data to ensure that SO2 in the air is at levels that protect public health and the environment. Nationally, average SO2 concentrations have decreased substantially over the years. For information on SO2 standards, sources, health effects, and programs to reduce SO2, please see www.epa.gov/air/sulfurdioxide/.

LeadNature and Sources of Lead

In the past, motor vehicles were the major contributor of lead emissions to the air. As a result of EPA's regulatory efforts to reduce lead in on-road motor vehicle gasoline, air emissions of lead from the

transportation sector, and particularly the automotive sector, have greatly declined over the past two decades.  Major sources of lead emissions to the air today are ore and metals processing and piston-engine aircraft operating on leaded aviation gasoline.  The highest air concentrations of lead are usually found near lead smelters.  Other stationary sources are waste incinerators, utilities, and lead-acid battery manufacturers.

HealthIn addition to exposure to lead in air, other major exposure pathways include ingestion of lead in drinking water and lead-contaminated food as well as incidental ingestion of lead-contaminated soil and dust. Lead-based paint remains a major exposure pathway in older homes.  Learn more about lead in paint, dust and soil.

Once taken into the body, lead distributes throughout the body in the blood and is accumulated in the bones.  Depending on the level of exposure, lead can adversely affect the nervous system, kidney function, immune system, reproductive and developmental systems and the cardiovascular system.  Lead exposure also affects the oxygen carrying capacity of the blood.  The lead effects most commonly encountered in current populations are neurological effects in children and cardiovascular effects (e.g., high blood pressure and heart disease) in adults.  Infants and young children are especially sensitive to even low levels of lead, which may contribute to behavioral problems, learning deficits and lowered IQ.

Lead is persistent in the environment and accumulates in soils and sediments through deposition from air sources, direct discharge of waste streams to water bodies, mining, and erosion.  Ecosystems near point sources of lead demonstrate a wide range of adverse effects including losses in biodiversity, changes in community composition, decreased growth and reproductive rates in plants and animals, and neurological effects in vertebrates.

National Trends in Lead Levels

Under the Clean Air Act, EPA sets and reviews national air quality standards for lead. Air quality monitors measure concentrations of lead throughout the country. EPA, state, tribal and local agencies use those data to ensure that lead is at levels that protect public health and the environment. EPA has tracked air quality trends for lead using data from this network of monitors. Trends from 1980-2009 and from 1990-2009 are shown here. Nationally, average lead concentrations decreased dramatically after EPA's regulations reduced the lead content in on-road motor vehicle gasoline. For information on lead standards, sources, health effects, and programs to reduce lead, please see www.epa.gov/air/lead and www.epa.gov/otaq/aviation.htm.

EPA projects that the Clean Air Act Amendments will prevent over 230,000 early deaths in 2020. Learn more about the Benefits and Costs of the Clean Air Act.

EPA is celebrating the 40th anniversary of the Clean Air Act. Learn more about how this landmark law has protected America's health and environment.

The Clean Air Act is the law that defines EPA's responsibilities for protecting and improving the nation's air quality and the stratospheric ozone layer. The last major change in the law, the Clean Air Act Amendments of 1990, was enacted by Congress in 1990. Legislation passed since then has made several minor changes.

The Clean Air Act, like other laws enacted by Congress, was incorporated into the United States Code as Title 42, Chapter 85. The House of Representatives maintains a current version of the U.S. Code, which includes Clean Air Act changes enacted since 1990.

This site provides links to sections of the U.S. Code containing the amended text of the Clean Air Act. Section numbers in the U.S. Code are different than the Clean Air Act's section numbers. The table of contents below gives corresponding section numbers in the Clean Air Act (CAA) and the U.S. Code (USC). Another difference is that titles in the Clean Air Act correspond to subchapters in the U.S. Code.

The legal authority for federal programs regarding air pollution control is based on the 1990 Clean Air Act Amendments (1990 CAAA). These are the latest in a series of amendments made to the Clean Air Act (CAA). This legislation modified and extended federal legal authority provided by the earlier Clean Air Acts of 1963 and 1970.

The Air Pollution Control Act of 1955 was the first federal legislation involving air pollution. This Act provided funds for federal research in air pollution. The Clean Air Act of 1963 was the first federal legislation regarding air pollution control. It established a federal program within the U.S. Public Health Service and authorized research into techniques for monitoring and controlling air pollution. In 1967, the Air Quality Act was enacted in order to expand federal government activities. In accordance with this law, enforcement proceedings were initiated in areas subject to interstate air pollution transport. As part of these proceedings, the federal government for the first time conducted extensive ambient monitoring studies and stationary source inspections.

The Air Quality Act of 1967 also authorized expanded studies of air pollutant emission inventories, ambient monitoring techniques, and control techniques.

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Clean Air Act of 1970

The enactment of the Clean Air Act of 1970 (1970 CAA) resulted in a major shift in the federal government's role in air pollution control. This legislation authorized the development of comprehensive federal and state regulations to limit emissions from both stationary (industrial) sources and mobile sources. Four major regulatory programs affecting stationary sources were initiated: the National Ambient Air Quality Standards (NAAQS, pronounced "knacks"), State Implementation Plans (SIPs), New Source Performance Standards (NSPS), and National Emission Standards for Hazardous Air Pollutants (NESHAPs). Furthermore, the enforcement authority was substantially expanded. The adoption of this very important legislation occurred at approximately the same time as the National Environmental Policy Act that established the U.S. Environmental Protection Agency (EPA). The EPA was created on May 2, 1971 in order to implement the various requirements included in the Clean Air Act of 1970.

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Clean Air Act Amendments of 1977

Major amendments were added to the Clean Air Act in 1977 (1977 CAAA). The 1977 Amendments primarily concerned provisions for the Prevention of Significant Deterioration (PSD) of air quality in areas attaining the NAAQS. The 1977 CAAA also contained requirements pertaining to sources in non-attainment areas for NAAQS. A non-attainment area is a geographic area that does not meet one or more of the federal air quality standards. Both of these 1977 CAAA established major permit review requirements to ensure attainment and maintenance of the NAAQS.

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Clean Air Act Amendments of 1990

Another set of major amendments to the Clean Air Act occurred in 1990 (1990 CAAA). The 1990 CAAA substantially increased the authority and responsibility of the federal government. New regulatory programs were authorized for control of acid deposition (acid rain) and for the issuance of stationary source operating permits. The NESHAPs were incorporated into a greatly expanded program for controlling toxic air pollutants. The provisions for attainment and maintenance of NAAQS were substantially modified and expanded. Other revisions included provisions regarding stratospheric ozone protection, increased enforcement authority, and expanded research programs.

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Milestones

Some principal milestones in the evolution of the Clean Air Act are:

The Air Pollution Control Act of 1955

First federal air pollution legislation

Funded research for scope and sources of air pollution

Clean Air Act of 1963

Authorized the development of a national program to address air pollution related environmental problems

Authorized research into techniques to minimize air pollution

Air Quality Act of 1967

Authorized enforcement procedures for air pollution problems involving interstate transport of pollutants

Authorized expanded research activities

Clean Air Act 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 Emission Standards for Hazardous Air Pollutants

Increased enforcement authority

Authorized requirements for control of motor vehicle emissions

1977 Amendments to the Clean Air Act of 1970

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

1990 Amendments to the Clean Air Act of 1970

Authorized programs for Acid Deposition Control

Authorized a program to control 189 toxic pollutants, including those previously regulated by the National Emission 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.