OUR NATION'S AIR

TRENDS THROUGH 2020

Welcome!

For more than 50 years, the U.S. Environmental Protection Agency (EPA) has maintained its commitment to protecting public health by reducing pollutant emissions and improving air quality. This annual report, titled Our Nation's Air, summarizes the nation's air quality status and trends through 2020.

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

Intro

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 78%. 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), and certain toxic air pollutants. 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).
Source: U.S. EPA National Emissions Inventory 2017

Air Pollution Can Affect Our Health and Environment in Many Ways

Numerous scientific studies have linked air pollution and specific pollutants to a variety of health problems and environmental impacts. 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 Oxides of nitrogen are a group of highly reactive gases, for which nitrogen dioxide (NO2) is the gas of greatest health concern. 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 environmental effects. Deposition of oxides of nitrogen contribute to the acidification and nutrient enrichment (eutrophication, nitrogen saturation) of soils and surface waters, ozone formation, as well to the direct and indirect effects on vegetation, soils, and animals.

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 Among the species of SOx, SO2 is the most commonly occurring in the atmosphere and the one most clearly associated with human 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.

Environmental Effects Sulfur oxides react with ammonia and other compounds to form particle pollution resulting in associated environmental effects. Deposition of sulfur oxides contributes to the acidification of soils and surface waters and mercury methylation in wetland areas. At certain concentrations, sulfur oxides can also cause injury to vegetation and species loss in aquatic and terrestrial systems.

Growth

For over 50 years, the Clean Air Act has played a major role in cutting pollution as the U.S. economy has grown. Despite the sharp impacts from the COVID-19 pandemic on activity in 2020, the U.S. economy remained strong.

Economic Strength with Cleaner Air

Between 1970 and 2020, the combined emissions of the six common pollutants (PM2.5 and PM10, SO2, NOx, VOCs, CO and Pb) dropped by 78 percent. This progress occurred while U.S. economic indicators remain strong.

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 2020.
Source: Various
Animated video background showing NASA satellite imagery of declining nitrogen dioxide levels across the contiguous 48 states from 2005 to 2020.

National Ambient Air Quality Standards (NAAQS)

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

of NASA 2005 - 2020 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 2000-2019 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.
Source: U.S. EPA Air Quality System

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 2000-2020. 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 2020. In 2000 the number of days was 2,076 and in 2020 641. Ozone and PM2.5 air quality index

A look back: Combined Ozone and PM2.5 in 2020

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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 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

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Visibility

Over its 50+ year history, EPA has made significant progress in protecting the magnificent views of America’s national treasures from pollution. State and federal governments are working together to improve the natural visibility in our nation’s parks and wilderness areas so that future generations can enjoy these scenic vistas.

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 most 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 2000-2019 trends, and select maximize to enlarge the chart. Double click the map to zoom in and click the home button to reset.

    Source: IMPROVE

    Air Toxics

    Following the 1990 Clean Air Act Amendments, significant improvements in public health protection occurred as a result of reductions in air toxics emissions from large industrial facilities and transportation.

    Spotlight

    Air quality is routinely impacted by numerous factors. In 2020, two extraordinary events impacted our nation's air quality. The COVID-19 pandemic contributed to improved air quality in many locations, especially in the springtime. On the flip-side, prolific wildfires in the Northwest and California led to increased particle pollution in the fall. These events brought about significant challenges for monitoring agencies. Our state and local partners are to be commended for their dedication in keeping air quality monitors up and running during this period.

    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 97 million Americans lived in counties with air quality concentrations above the level of one or more NAAQS in 2020.
    The downloadable EPA air trends infographic has four graphics depicting improving air quality trends since 1970. The top left chart shows the 272 percent increase of the United States gross domestic product against a 78 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 69 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.

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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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