United States Environmental Protection Agency
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The U.S. Environmental Protection Agency (EPA) is committed to protecting public health by improving air quality and reducing air pollution. This annual report presents the trends in the nation's air quality, and summarizes the detailed information found at EPA's AirTrends website (link will open in a new tab).

Please scroll down to view the annual report 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

The U.S. leads the world in having clean air and a strong economy due to implementation of the Clean Air Act and technological advancements from American innovators. Cleaner air provides important public health benefits.

Air Quality Improves as America Grows

Nationally, concentrations of the criteria and hazardous air pollutants have dropped significantly since 1990:

  • Carbon Monoxide (CO) 8-Hour, 77%
  • Lead (Pb) 3-Month Average, 99%
  • Nitrogen Dioxide (NO2) Annual, 56%
  • Nitrogen Dioxide (NO2) 1-Hour, 50%
  • Ozone (O3) 8-Hour, 22%
  • Particulate Matter 10 microns (PM10) 24-Hour, 39%
  • Particulate Matter 2.5 microns (PM2.5) Annual, 42%
  • Particulate Matter 2.5 microns (PM2.5) 24-Hour, 44%
  • Sulfur Dioxide (SO2) 1-Hour, 85%
  • Numerous air toxics have declined with percentages varying by pollutant

During this same period, the U.S. economy continued to grow, Americans drove more miles and population and energy use increased.

Tip Click pollutant names in the chart legend to hide or include trend lines, and hover over any line to display percentages above or below the most recent standard. Click the emission trends button below to open a popup window.

Line chart depicting overall decline in national air quality concentration averages for the criteria air pollutants from 1990 to 2016.

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.

Playground with emissions stack in background

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.

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. People at greater risk for experiencing air pollution-related health effects may, depending on the pollutant, include older adults, children and those with heart and respiratory diseases — 30-second Healthy Heart video (link will open in a new tab).

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 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 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.

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 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 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 (see above).

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 (see above).

For more than forty 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 2016, the combined emissions of the six common pollutants (PM2.5 and PM10, SO2, NOx, VOCs, CO and Pb) dropped by 73 percent. This progress occurred while the U.S. economy continued to grow, Americans drove more miles and population and energy use increased.

To learn more about the EPA and environmental milestones to reduce pollution please visit the EPA history website (link will open in a new tab).

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 2016.
Animated video background showing NASA satellite imagery of declining nitrogen dioxide levels across the contiguous 48 states from 2005 to 2016.

Today Americans breathe cleaner air and face lower risks of adverse health effects.

2005 - 2016 NO2 satellite imagery courtesy of NASA

Criteria Pollutant Trends Show Clean Air Progress

Based on NAAQS dropdown selection, a synchronized set of charts (air quality concentration chart, emissions stacked area chart and USA map of monitor locations) display. The first is a line chart depicting the overall decline in national air quality concentrations for criteria air pollutants from 1990 to 2016. The chart provides national concentration averages, 10th and 90th percentiles, and minimum and maximum values for each year.
    Based on previous NAAQS dropdown selection: Stacked area chart depicting the corresponding national air emissions by the source categories of stationary fuel combusion, industrial and other processes, highway vehicles and non-road mobile from 1990 to 2016.

    Charts Click emission tabs to change the emissions chart. The play/pause button controls animation, or manually change the year by dragging the yellow circle in the chart or the slider's gray square. Read about weather influences on ozone (link will open in a new tab).

    Pressing the play button animates the synchronized charts and map cycling through 1990 to 2016 showing how both concentrations and emissions are changing, with a declining overall trend, during this period.
    Year: 2000 Start animation Pause animation
    Based on previous NAAQS dropdown selection: USA map of corresponding monitor locations with information for each monitor such as Air Quality System (AQS) site ID, State, overall trend, annual concentration data and year.

    Map Symbols indicate values above or below the most recent standard. Click any point to display annual concentration data. Double click the map to zoom in and click the home button to reset. Please be patient with map exports.

    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.

    Click any point to display 2006-2015 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 2006 to 2015 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 Quality Days Trending Down

    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.

    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 2000-2016. Click the bar chart, or these links, to view the AQI retrospective reviews: PM2.5 and ozone (links will open in a new tab).

    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 2016. Ozone and PM2.5 air quality index

    A look back: Combined Ozone and PM2.5 in 2016


    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.

    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


    EPA has made significant progress in improving visibility in our nation's parks and wilderness areas.

    Visibility Improves in Scenic Areas

    The National Park Service celebrated 100 years on August 25, 2016. Together, EPA and other agencies 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 and EPA's visibility story map (links will open in a new tab).

    Click any point to display 2000-2015 trends, and select maximize to enlarge the chart. Double click the map to zoom in and click the home button to reset.

    EPA works with state, local and tribal governments to reduce emissions of 187 hazardous air pollutants.

    Air Toxics Levels Trending Down

    Ambient monitoring data show that some of the toxic air pollutants, such as benzene, 1,3-butadiene and several metals, are declining at most sites.

    Points on the map indicate the long-term statistical trend direction: decreasing, increasing and no trend. Depicted in gray are sites where a trend direction is undetermined due to insufficient data.

    Use the dropdown menu to select a pollutant, click any point to display trends, and select maximize to enlarge the chart. Double click the map to zoom in and click the home button to reset. View a tabular summary of air toxics trends (link will open in a new tab).

    The NATTS trends table, included as a supplementary visual to the USA map, depicts air toxics mean concentration trends at the 27 national air toxics trends stations from 2003 to 2015. A majority of stations show decreasing or no trend in air toxics across the country.
    USA map depicting air toxics mean concentration trends from 2003 to 2015 at the 27 national air toxics trends stations and numerous other monitors tracking air toxics. A vast majority of stations show decreasing or no trend in air toxics across the country.

    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.

    Highlights from this report are available for download by clicking the icon in the top menu.

    The downloadable EPA air trends infographic has four graphics depicting improving air quality trends since 1970. The top left chart shows the 253 percent increase of the United States gross domestic product against a 73 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 66 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.

    Additional Resources

    Please visit other EPA air quality related websites.