Environments and Contaminants - Criteria Air Pollutants
The six most common air pollutants are called “criteria” air pollutants and include carbon monoxide (CO), lead (Pb), ground-level ozone (O3), particulate matter (PM), nitrogen dioxide (NO2), and sulfur dioxide (SO2).
Indicators
Percentage of children ages 0 to 17 years living in counties with pollutant concentrations above the levels of the current air quality standards, 1999-2021 (Indicator E1)
Web update: 2023
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Data characterization
- Data for this indicator are obtained from EPA’s Air Quality System (AQS) database.
- Ambient air monitors are placed in locations throughout the United States, with an emphasis on areas expected to have higher pollutant concentrations or that have larger populations. Not all counties in the United States have air pollution monitors.
- To support long-term trends and other data uses, monitors generally tend to stay in the same location over many years, but there may be some limited changes in the number or location of monitors providing data from year to year.
- From 1999 to 2021, the percentage of children living in counties with measured pollutant concentrations above the levels of one or more national ambient air quality standards decreased from 76% to 59%. This includes both concentrations above the level of any current short-term standard at least once during the year as well as average concentrations above the level of any current long-term standards. The decreasing trend over the years 1999–2021 was statistically significant.
- From 1999–2021, the percentage of children living in counties with measured concentrations above the level of the current 8-hour ozone standard at least one day during the year decreased from 66% to 51%. The decreasing trend for ozone over the years 1999–2021 was statistically significant.
- From 1999–2021, the percentage of children living in counties with measured PM2.5 concentrations above the level of the current 24-hour PM2.5 standard at least once per year decreased from 55% in 1999 to 34% in 2021. Over the same years, the percentage of children living in counties with a measured concentration above the level of the current PM2.5 annual standard decreased from 37% in 1999 to 8% in 2021. The decreasing trends for PM2.5 over the years 1999-2021 were statistically significant.
- From 1999–2021, the percentage of children living in counties with measured sulfur dioxide concentrations above the level of the current one-hour standard for sulfur dioxide at least one day per year declined from 31% to 2%. Over the same years, the percentage of children living in counties with measured concentrations above the level of the current one-hour standard for nitrogen dioxide at least one day per year declined from 23% to less than 1%. The decreasing trends for both sulfur dioxide and nitrogen dioxide over the years 1999-2021 were statistically significant.
- In 2021, 13% of children lived in counties with measured PM10 concentrations above the level of the current 24-hour standard for PM10 at least one day per year, no children lived in counties with measured concentrations above the level of the current standard for carbon monoxide, and 1 county with 0.1% of U.S. children reported concentrations above the level of the three-month standard for lead.
- Almost 75% of Asian non-Hispanic children lived in counties in which air quality standards for any pollutant were exceeded in 2021, followed by Hispanic children (73%), Two or More Races (60%), Black non-Hispanic (59%), Native Hawaiian and Other Pacific Islander (58%), White non-Hispanic (51%), and Native American/Alaska Native non-Hispanic (48%). (See Indicator E1a.)
Percentage of children ages 0 to 17 years living in counties with 8-hour ozone and 24-hour PM2.5 concentrations above the levels of air quality standards, by frequency of occurrence, 2021 (Indicator E2)
Web update: 2023
Click to open in new window | Tips for selecting and filtering data (pdf) | Download in Excel
Data characterization
- Data for this indicator are obtained from EPA’s Air Quality System (AQS) database.
- Ambient air monitors are placed in locations throughout the United States, with an emphasis on areas expected to have higher pollutant concentrations or that have larger populations. Not all counties in the United States have air pollution monitors.
- In 2021, 31% of children lived in counties with no monitoring data for PM2.5 and 26% of children lived in counties with no monitoring data for ozone.
- The ozone 8-hour standard was adopted in July 1997, changed from 0.08 to 0.075 ppm in March 2008, and changed again from 0.075 to 0.070 ppm in October 2015.
- The PM2.5 24-hour standard was revised from 65 µg/m3 to 35 µg/m3 in 2006. The PM2.5 annual standard was revised from 15 µg/m3 to 12 µg/m3 in 2012. See the Detailed Methods for additional information.
- In 2021, 1% of children lived in counties with measured PM2.5 concentrations above the level of the 24-hour PM2.5 standard on more than 25 days, 6% of children lived in counties with measured concentrations above the level of the 24-hour PM2.5 standard between 11 and 25 days, and 2% of children lived in counties with measured concentrations above the level of the 24-hour PM2.5 standard between 8 and 10 days.
- In 2021, 9% of children lived in counties with measured ozone concentrations above the level of the 8-hour ozone standard on more than 25 days, 8% of children lived in counties with measured concentrations above the level of the ozone standard between 11 and 25 days, and 13% of children lived in counties with measures concentrations above the level of the ozone standard between 4 and 10 days.
- In 1999, 6% of children lived in counties with measured PM2.5 concentrations above the level of the current 24-hour PM2.5 standard on more than 25 days, 11% of children lived in counties with measured concentrations above the level of the current 24-hour PM2.5 standard between 11 and 25 days, and 1% of children lived in counties with measured concentrations above the level of the 24-hour PM2.5 standard between 8 and 10 days.
- In 1999, 38% of children lived in counties with measured ozone concentrations above the level of the current 8-hour ozone standard on more than 25 days, 20% of children lived in counties with measured concentrations above the level of the current 8-hour ozone standard between 11 and 25 days, and 8% of children lived in counties with measures concentrations above the level of the current 8-hour ozone standard between 4 and 10 days.
Percentage of days with good, moderate, or unhealthy air quality for children ages 0 to 17 years, 1999-2021 (Indicator E3)
Web update: 2023
Click to open in new window | Tips for selecting and filtering data (pdf) | Download in Excel
Data characterization
- Data for this indicator are obtained from EPA's Air Quality System (AQS) database.
- Ambient air monitors are placed in locations throughout the country, with an emphasis on areas expected to have higher pollutant concentrations or that have larger populations. Not all counties in the United States have air pollution monitors.
- AQI values are based on daily monitoring data for up to five criteria air pollutants. Some counties do not have monitors, and some monitors do not operate every day, so some days do not have AQI values for every pollutant every day.
- For this indicator, the available monitoring data are used to assign a value of “good,” “moderate,” “unhealthy,” or “no monitoring data” for each day in each U.S. county. The “unhealthy” category used in Indicator E3 represents all AQI categories above 100, including Unhealthy for Sensitive Groups, Unhealthy, Very Unhealthy, and Hazardous.
- The percentage of children’s days that were designated as having “unhealthy” air quality decreased from 10% in 1999 to 4% in 2021. The percentage of children’s days with “good” air quality increased from 38% in 1999 to 53% in 2021. The percentage of children’s days with “moderate” air quality decreased from 24% in 1999 to 22% in 2021. The 1999 to 2021 trends in “unhealthy,” “good,” and “moderate” air quality days were statistically significant.
- In 2021, considering only days with monitoring data, good air quality days were highest for White children at 73% and lowest for Hispanic children at 58%. (See Indicator E3a.)
- In 2021, considering only days with monitoring data, the percentage of days with good air quality for children was 66% for children in families with income below poverty level and 68% for children in families with income at or above poverty level. (See Indicator E3b.)
About the Criteria Air Pollutants Indicators
Indicators E1 and E2 present information about children living in counties with air pollutant concentrations above the level of air quality standards and Indicator E3 presents information about air quality ratings across all United States counties each year. The data for Indicators E1 and E2 are from a database that compiles air monitoring measurements from around the United States each year. The data for Indicator E3 are from a database that provides a rating of the air quality for each United States county on each day.
Air pollution contributes to a wide variety of adverse health effects. The six most common air pollutants are called “criteria” air pollutants and include carbon monoxide, lead, ground-level ozone, particulate matter, nitrogen dioxide, and sulfur dioxide. Exposure to these pollutants has been associated with health effects like coughing and wheezing, aggravation of respiratory illnesses such as asthma, and neurodevelopmental effects (for lead). Children may be particularly susceptible to adverse effects because their lungs and other organ systems are still developing and because they may experience higher exposure due to their activities such as outdoor play.
EPA has established national ambient air quality standards (NAAQS) for the criteria pollutants. The standards are set at a level to protect public health, including the health of at-risk populations such as children. Some of the standards are designed to protect against adverse health effects that can happen after exposure for a short time (e.g., ozone concentrations averaged over 8 hours) and others are designed to protect against effects from more long term exposure (e.g., rolling three month lead concentrations).
Indicators E1 and E2 present data on children living in counties with concentrations of criteria pollutants above the levels of the standards from the EPA Air Quality System (AQS) database. Indicator E3 presents data on air quality for children from EPA’s Air Quality Index (AQI).
More information about criteria air pollutants and Indicators E1, E2, and E3 is provided in the Criteria Air Pollutants section of America's Children and the Environment, Third Edition (pdf) .
Methods - Criteria Air Pollutants
EPA, state, local, and tribal air pollution control agencies collect and report data from thousands of monitors to the Air Quality System (AQS) database. For Indicators E1 and E2, these criteria pollutant measurements are compared to the levels of the National Ambient Air Quality Standards (NAAQS), established by EPA under the Clean Air Act. Indicator E3 uses EPA’s Air Quality Index (AQI), which is calculated from data in the AQS database. The AQI is based on daily measurements of all the criteria pollutants except for lead.
Indicator E1 uses the AQS data to present the percentage of children ages 0 to 17 years living in counties that have measured concentrations of a pollutant greater than the level of the current NAAQS for each criteria pollutant. Indicator E2 uses the AQS data to present the percentage of children ages 0 to 17 years living in counties that have measured concentrations greater than the level of the current NAAQS for two particular criteria air pollutants: ozone and PM2.5.
Indicator E3 uses the AQI to present the percentage of days in each year considered to be in the categories of “good,” “moderate,” or “unhealthy” air quality for children ages 0 to 17 years.
- Detailed Methods for Indicators E1, E2, and E3 (pdf)
- Air Quality System (AQS) Metadata (pdf)
- Metadata for Census: Decennial Data (pdf)
- Metadata for Census: Intercensal and Postcensal Data