The environment in which children live plays an important role in their health and development. Children may be more vulnerable than adults to the adverse effects of environmental contaminants in air, food, drinking water, and other sources because their bodies are still developing. In addition, children have increased potential for exposure to pollutants because they eat, drink, and breathe more, in proportion to the size of their bodies, than adults. One important measure of children's environmental health is the percentage of children living in areas in which air pollution levels are higher than the allowable levels of the Primary National Ambient Air Quality Standards.⁵³ These standards, established by the U.S. Environmental Protection Agency under the Clean Air Act, are designed to protect public health, including the health of susceptible populations such as children. Ozone, particulate matter, sulfur dioxide, and nitrogen dioxide are air pollutants associated with increased asthma episodes and other respiratory illnesses in children. These problems can lead to increased emergency room visits and hospitalizations.^{54, 55, 56, 57} Lead can affect the development of the central nervous system in young children,⁵⁸ and exposure to carbon monoxide can reduce the capacity of blood to carry oxygen.⁵⁹

Indicator PHY1: Percentage of children ages 0–17 living in counties with pollutant concentrations above the levels of the current air quality standards, 1999–2021

• From 1999 to 2021, the percentage of children living in counties with measured pollutant concentrations above the levels of one or more Primary National Ambient Air Quality Standards at least once during the year decreased from 76% to 59%.
• From 1999 to 2021, the percentage of children living in counties with measured ozone concentrations above the level of the current ozone standard at least 1 day during the year decreased from 66% to 51%.
• In 2021, approximately 34% of children lived in counties with measured concentrations of fine particulate matter (PM2.5) above the level of the current 24-hour PM2.5 standard at least once during the year compared with 55% of children in 1999.
• From 1999 to 2021, the percentage of children living in counties with measured sulfur dioxide concentrations above the level of the current standard for sulfur dioxide at least 1 day per year declined from 31% to 2%. During the same time frame, the percentage of children living in counties with measured concentrations above the level of the current standard for nitrogen dioxide at least 1 day per year decreased from 23% to 0%.
• In 2021, the percentage of children living in counties with measured pollutant concentrations above the levels of one or more Primary National Ambient Air Quality Standards at least once during the year by race/ethnicity was 48% for American Indian or Alaska Native, non-Hispanic children; 51% for White, non-Hispanic children; 58% for Native Hawaiian and Other Pacific Islander, non-Hispanic children; 59% for Black, non-Hispanic children; 60% for children of two or more races; 75% for Asian, non-Hispanic children; and 73% for Hispanic children.

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