EPA Celebrates 50 Years!


For 50 years, the U.S. Environmental Protection Agency (EPA) has maintained its commitment to protecting public health by improving air quality and reducing air pollution. This annual report, titled Our Nation's Air, summarizes the nation's air quality status and trends through 2019.

Sections of this report convey information across different time periods, depending on the underlying data sources. While some are consistently available since 1970, like growth data, our longer-term trends for air quality concentrations start in 1990, when monitoring methodologies became more consistent.

Please read and enjoy the full report below, and be sure to download and share the one page summary using the share button at the top. Additional detail on air trends can be found at EPA's AirTrends website.

Scroll down to read more or use the top menu to jump to a topic. If you encounter any issues viewing content, update or try opening the website in another browser.

United States Environmental Protection Agency

Since 1970, implementation of the Clean Air Act and technological advances from American innovators have dramatically improved air quality in the U.S. Since that time, the combined emissions of criteria and precursor pollutants have dropped by 77%. Cleaner air provides important public health benefits, and we commend our state, local, and industry partners for helping further long-term improvement in our air quality.

Air Pollution Includes Gases and Particles

Air pollution consists of gas and particle contaminants that are present in the atmosphere. Gaseous pollutants include sulfur dioxide (SO2), oxides of nitrogen (NOx), ozone (O3), carbon monoxide (CO), volatile organic compounds (VOCs), certain toxic air pollutants and some gaseous forms of metals. Particle pollution (PM2.5 and PM10) includes a mixture of compounds that can be grouped into five major categories: sulfate, nitrate, elemental (black) carbon, organic carbon and crustal material.

Some pollutants are released directly into the atmosphere while other pollutants are formed in the air from chemical reactions. Ground-level ozone forms when emissions of NOx and VOCs react in the presence of sunlight. Air pollution impacts human health and the environment through a variety of pathways.

17 second animation showing air pollution pathways. Depicts cycle of sources, transport and transformation, deposition and effects.

Understanding Emission Sources Helps Control Air Pollution

Generally, emissions of air pollution come from

  • stationary fuel combustion sources (such as electric utilities and industrial boilers),
  • industrial and other processes (such as metal smelters, petroleum refineries, cement kilns and dry cleaners),
  • highway vehicles, and
  • non-road mobile sources (such as recreational and construction equipment, marine vessels, aircraft and locomotives).

As the chart shows, pollutants are emitted by a variety of sources. For example, electric utilities, part of the stationary fuel combustion category, release SO2, NOx and particles.

Tip Click source categories in the chart legend to hide or include, and hover over any bar to display totals or percentages by source category. Click the ellipsis in the upper righthand corner and check "Show Totals" to view the chart based on totals instead of percentages.

Bar chart depicting total national emissions and percentages by source category (stationary fuel combustion, industrial and other processes, highway vehicles and non-road mobile).

Air Pollution Can Affect Our Health and Environment in Many Ways

Numerous scientific studies have linked air pollution to a variety of health problems. Depending on the pollutant, people at greater risk for experiencing air pollution-related health effects may include older adults, children and those with heart and respiratory diseases — 30-second Healthy Heart video.

Health Effects Breathing elevated levels of CO reduces the amount of oxygen reaching the body’s organs and tissues. For those with heart disease, this can result in chest pain and other symptoms leading to hospital admissions and emergency department visits.

Environmental Effects Emissions of CO contribute to the formation of CO2 and ozone, greenhouse gases that warm the atmosphere.

Health Effects Air toxics may cause a broad range of health effects depending on the specific pollutant, the amount of exposure, and how people are exposed. People who inhale high levels of certain air toxics may experience eye, nose and throat irritation, and difficulty breathing. Long term exposure to certain air toxics can cause cancer and long-term damage to the immune, neurological, reproductive, and respiratory systems. Some air toxics contribute to ozone and particle pollution with associated health effects.

Environmental Effects Some toxic air pollutants accumulate in the food chain after depositing to soils and surface waters. Wildlife and livestock may also be harmed with sufficient exposure. Some toxic air pollutants contribute to ozone and particle pollution with associated environmental and climate effects.

Health Effects Depending on the level of exposure, lead may harm the developing nervous system of children, resulting in lower IQs, learning deficits and behavioral problems. Longer-term exposure to higher levels of lead may contribute to cardiovascular effects, such as high blood pressure and heart disease in adults.

Environmental Effects Elevated amounts of lead accumulated in soils and fresh water bodies can result in decreased growth and reproductive rates in plants and animals.

Health Effects Short-term exposures to NO2 can aggravate respiratory diseases, particularly asthma, leading to respiratory symptoms, hospital admissions and emergency department visits. Long-term exposures to NO2 may contribute to asthma development and potentially increase susceptibility to respiratory infections.

Environmental Effects Oxides of nitrogen react with volatile organic compounds to form ozone and react with ammonia and other compounds to form particle pollution resulting in associated public health and environmental effects. Deposition of nitrogen oxides contributes to the acidification and nutrient enrichment (eutrophication, nitrogen saturation) of soils and surface waters. These effects can change the diversity of ecosystems.

Deposition of sulfur oxides contributes to the acidification of soils and surface waters and mercury methylation in wetland areas. Sulfur oxides cause injury to vegetation and species loss in aquatic and terrestrial systems and contribute to particle formation with associated environmental effects. Sulfate particles contribute to the cooling of the atmosphere.

Health Effects Ozone exposure reduces lung function and causes respiratory symptoms, such as coughing and shortness of breath. Ozone exposure also aggravates asthma and lung diseases such as emphysema leading to increased medication use, hospital admissions, and emergency department visits. Exposure to ozone may also increase the risk of premature mortality from respiratory causes. Short-term exposure to ozone is also associated with increased total non-accidental mortality, which includes deaths from respiratory causes.

Environmental Effects Ozone damages vegetation by injuring leaves, reducing photosynthesis, impairing reproduction and growth and decreasing crop yields. Ozone damage to plants may alter ecosystem structure, reduce biodiversity and decrease plant uptake of CO2. Ozone is also a greenhouse gas that contributes to the warming of the atmosphere.

Health Effects Exposures to PM, particularly fine particles referred to as PM2.5, can cause harmful effects on the cardiovascular system including heart attacks and strokes. These effects can result in emergency department visits, hospitalizations and, in some cases, premature death. PM exposures are also linked to harmful respiratory effects, including asthma attacks.

Environmental Effects Fine particles (PM2.5) are the main cause of reduced visibility (haze) in parts of the U.S., including many national parks and wilderness areas. PM can also be carried over long distances by wind and settle on soils or surface waters. The effects of 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. PM can stain and damage stone and other materials, including culturally important objects such as statues and monuments.

Health Effects Short-term exposures to SO2 are linked with respiratory effects including difficulty breathing and increased asthma symptoms. These effects are particularly problematic for asthmatics while breathing deeply such as when exercising or playing. Short-term exposures to SO2 have also been connected to increased emergency department visits and hospital admissions for respiratory illnesses, particularly for at-risk populations including children, older adults and those with asthma. SO2 contributes to particle formation with associated health effects.


For nearly 50 years, the Clean Air Act has been a key part of cutting pollution as the U.S. economy has grown.

Economic Growth with Cleaner Air

Between 1970 and 2019, the combined emissions of the six common pollutants (PM2.5 and PM10, SO2, NOx, VOCs, CO and Pb) dropped by 77 percent. This progress occurred while the U.S. economy continued to grow, Americans drove more miles, and population and energy use increased.

Tip Click any of the legend items on the right side of the chart to hide or include trend lines. The y-axis may change based on the selections.

Line chart depicting comparisons of growth areas such as gross domestic product, vehicle miles traveled, population, energy consumption, carbon dioxide emissions versus the decline in the aggregate emissions of the six common pollutants from 1970 to 2019.
Animated video background showing NASA satellite imagery of declining nitrogen dioxide levels across the contiguous 48 states from 2005 to 2019.

For nearly 50 years, the Clean Air Act has brought Americans cleaner air and lower risks of adverse health effects.

of NASA 2005 - 2019 NO2 satellite imagery

Understanding PM2.5 Composition Helps Reduce Fine Particle Pollution

The different components that make up particle pollution come from specific sources and are often formed in the atmosphere. The major components, or species, are elemental carbon (EC), organic carbon (OC), sulfate and nitrate compounds, and crustal materials such as soil and ash.

As previously shown, PM2.5 concentrations are declining. Assessing particle pollution concentrations along with composition data aids in understanding the effectiveness of pollution controls and in quantifying the impacts to public health, regional visibility, ecology and climate.

Tip Click any point to display 2000-2018 annual and quarterly PM2.5 speciation trends, and select maximize to enlarge the chart. Double click the map to zoom in and click the home button to reset.

USA map with PM2.5 speciation monitors depicted. Clicking a point opens a stacked bar graph depicting the 2000 to 2018 trends in PM2.5 speciation by component: sulfate, nitrate, elemental carbon, organic carbon, crustal material and sea-salt. Charts are available for each calendar year quarter, as well as an annual chart.

Unhealthy Air Days Show Long-Term Improvement

The Air Quality Index (AQI) is a color-coded index EPA uses to communicate daily air pollution for ozone, particle pollution, NO2, CO and SO2. A value in the unhealthy range, above the national air quality standard for any pollutant, is of concern first for sensitive groups, then for everyone as the AQI value increases. Fewer unhealthy air quality days means better health, longevity, and quality of life for all of us.

Tip Shown are the number of days in which the combined ozone and PM2.5 AQI was unhealthy for sensitive groups (orange) or above (red, purple or maroon) for the years 2000-2019. Click the bar chart, or these links, to view AQI retrospective reviews: PM2.5 or ozone.

Unhealthy air quality days vary year to year, influenced not only by pollution emissions but also by natural events, such as dust storms and wildfires , and variations in weather.
Image of bar chart depicting the declining number of days reaching unhealthy for sensitive groups, or above, on the air quality index from 2000 to 2019. In 2000 the number of days was 2,076 and in 2019 479. Ozone and PM2.5 air quality index

A look back: Combined Ozone and PM2.5 in 2019


Air Quality in Nonattainment Areas Improves

EPA works collaboratively with state, local and tribal agencies to identify areas of the U.S. that do not meet the national ambient air quality standards (NAAQS). These areas, known as nonattainment areas, must develop plans to reduce air pollution and attain the NAAQS.

Through successful state led implementation, numerous areas across the country are showing improvement and fewer areas are in nonattainment. Since 2010, there were no violations of the standards for CO and NO2.

Tip Shown is a snapshot of the 2008 ozone nonattainment area map. Click the map to view a larger interactive version that includes all current NAAQS nonattainment areas.

Image of map depicting the nonattainment areas for ozone. Click to open nonattainment areas story map in another browser window. 2008 Ozone Nonattainment Areas

Nonattainment Areas


Over its 50-year history, EPA has made significant progress in improving visibility in our nation's parks and wilderness areas.

Visibility Improves in Scenic Areas

EPA and other agencies, such as the National Park Service, monitor visibility trends in 155 of the 156 national parks and wilderness areas (i.e., Class I areas).

The map indicates several Class I areas have improving visibility or decreasing haze (indicated by the downward pointing arrows). To learn more about visibility in parks and view live webcams please visit this National Park Service website.

Tip Click any point to display 2000-2018 trends, and select maximize to enlarge the chart. Double click the map to zoom in and click the home button to reset.


    Following the 1990 Clean Air Act Amendments, key milestones in EPA's 50-year history were reached in significantly reducinig toxic emissions from industry and transportation.


    Since the early 1970s, EPA has prioritized monitoring air quality and informing Americans of progress and challenges in combatting air pollution to protect our health.

    EPA 50th Anniversary

    EPA was established on December 2, 1970 to consolidate in one agency a variety of federal research, monitoring, standard-setting and enforcement activities to ensure environmental protection. For 50 years, EPA has been working for a cleaner, healthier environment for the American people. EPA and its partners' actions have resulted in cleaner air, purer water and better protected land. The agency will continue its mission to protect human health and the environment for generations to come.

    Read more about EPA history, and EPA today, at the EPA at 50: Progress for a Stronger Future website.

    Tip Select a year at the top of the timeline, or click and drag photos left/right, to navigate through air quality milestones.

    Air Quality Milestones


    EPA and Clean Air Act Creation

    December 2, 1970 - EPA is officially established.

    December 31, 1970 - Congress passes the Clean Air Act of 1970 authorizing EPA to set national air quality, auto emission, and anti-pollution standards.


    National Air Quality Standards

    April 30, 1971 - EPA announces national standards on six common pollutants: sulfur oxides, particulate matter, carbon monoxide, photochemical oxidants, nitrogen oxides and hydrocarbons.


    Clean Air Act Amendments

    August 8, 1977 - President Jimmy Carter signs the Clean Air Act Amendments to further strengthen air quality standards and protect human health.


    New cars meet amended Clean Air Act standards for the first time

    Sophisticated three-way catalysts with on-board computers and oxygen sensors appear in most new cars, helping to optimize the efficiency of the catalytic converter. The automotive catalytic converter is considered one of the great environmental inventions of all time.


    Ozone Layer Depletion

    May 16, 1985 - A British Antarctic Survey team discovers a 7.3 million square mile ozone hole over Antarctica, marking the first evidence of stratospheric ozone depletion.


    International Partnership

    September 16, 1987 - President Ronald Reagan signs the Montreal Protocol, joining international partners in the first efforts to protect the ozone layer.


    CAA Amendments of 1990

    November 15, 1990 - Congress passes and President George H. W. Bush signs the Clean Air Act Amendments of 1990, which imposed a new cap and trade approach to addressing acid rain by reducing sulfur dioxide emissions, and implemented controls to phase out ozone-depleting substances, like CFCs.


    Science Behind Radon Risks and Tobacco Smoke

    May 1992 - EPA publishes the science behind radon risks showing radon was estimated to cause 14,000 lung cancer deaths each year in the US, making it the second leading cause of lung cancer after smoking.

    December 1992 - EPA concludes environmental tobacco smoke harms the health of smokers and those nearby leading to protections from secondhand smoke.


    EPA Online

    November 10, 1994 - EPA's first World Wide Web pages are posted, marking the start of increased public access to EPA programs, services, and environmental information and reports such as this one.


    Acid Rain Program Begins

    The Acid Rain Program (ARP) set an annual cap on the total amount of SO2 emitted by covered power plants and addressed NOX emissions at a subset of coal-fired power plants. There have been significant reductions in total sulfur deposition achieved by emissions control programs like the ARP. Read our progress report to learn more.


    Unleaded Gasoline

    EPA completes its 25-year mission to completely remove lead from gasoline. Lead is banned from gasoline as of January 1, 1996.


    Lead Phaseout Achieves Results

    Thanks to the phaseout of leaded gasoline from 1970 to 1996, levels of lead in the air decreased 94 percent between 1980 and 1999.


    Clearing the Air: Asthma and Indoor Air Exposure

    This seminal review formed the foundation for environmental controls as part of the national asthma care guidelines. The report describes the role of indoor environmental pollutants in the development and exacerbation of asthma. The report concludes that exposure to indoor pollutants is an important contributor to the asthma problem in this nation. EPA commissioned this National Academy of Science Report in 1999.


    Particle Pollution Standards

    September 21, 2006 - EPA issues the strongest national air quality standards for particle pollution in our country's history. The new standards protect public health and our nation's ecosystems and national treasures from dangerous soot and smog.


    airPLUS Label

    October 2008 - EPA Launches Indoor airPLUS Label for New Homes: Indoor airPLUS is a voluntary partnership and labeling program that helps new home builders improve the quality of indoor air by requiring construction practices and product specifications that minimize exposure to airborne pollutants and contaminants.


    Air Toxics

    December 21, 2011 - EPA issues the Mercury and Air Toxics Standards, the first national standards to protect American families from power plant emissions of mercury and toxic air pollution like arsenic, acid gas, nickel, selenium, and cyanide.


    Cleaner Fuel

    EPA finalizes Tier 3 Standards for gasoline and the vehicles passenger cars, light-duty trucks, medium-duty passenger vehicles, and some heavy-duty vehicles. Starting in 2017, Tier 3 sets new vehicle emissions standards and lowers the sulfur content of gasoline, considering the vehicle and its fuel as an integrated system. Light duty vehicles are now more than 99 percent cleaner than their 1970 counterparts.


    Our Nation's Air Online

    July 21, 2016 - EPA publishes its first online and interactive annual air trends report Our Nation's Air.

    Use the share button at the top of this report to post, tweet and email Our Nation's Air to friends and family.


    Cleaner Power Plants

    In 2019, coal-fired power plant emissions of SO2 dropped under a million tons for the first time. Learn more about Power Plant Emissions Trends .


    50 Years

    December 2, 2020 - EPA celebrates 50 years protecting human health and the environment! Interact with this timeline and visit the epa.gov/history website to learn more.

    Our Nation's Air Continues to Improve

    However, work must continue to ensure healthy air for all communities. EPA and our partners at the state, tribal and local levels will continue to work to address the complex air quality problems we face.

    Download and share the one page summary and scroll down for additional resources.

    Approximately 82 million Americans lived in counties with air quality concentrations above the level of one or more NAAQS in 2019.
    The downloadable EPA air trends infographic has four graphics depicting improving air quality trends since 1970. The top left chart shows the 285 percent increase of the United States gross domestic product against a 77 percent drop in air pollutant emissions since 1970. The top right chart shows decreasing national average ozone and particulate matter concentrations since 1990 with the averages falling below the most recent standard. The bottom right chart shows the 77 percent reduction in unhealthy air quality days from 2000. And the bottom left chart shows the descreasing emissions from 1990 for sulfur dioxide, nitrous oxides, volatile organic compounds, direct particulate matter and carbon monoxide.

    Social Media

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    Source code, data and documentation are available for download in the GitHub repository.

    Additional Resources

    Please visit other EPA air quality related websites.

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