The National Park Service (NPS) monitors ozone in parks around the country. The interactive map on this page shows the number of days that exceed National Ambient Air Quality Standard for ozone by park. This standard is set by the Environmental Protection Agency and identifies the level at which ozone in the air becomes unhealthy.
The map below displays the parks and the number of days where ozone levels have exceeded the standard in each year from 2016–2021. Monthly summaries of exceedance days as well as the maximum and 4th highest 8-hour average ozone concentrations are also provided by park. Click on park symbols to see this information.
The current National Ambient Air Quality Standard for ozone is of 70 parts per billion (ppb), daily maximum 8-hour average ozone concentration. An exceedance day occurs on each calendar day when the daily maximum 8-hour average is greater than or equal to 71 ppb. The ozone standard is violated when the 3-year average of the annual fourth-highest daily maximum 8-hour average ozone concentration is greater than or equal to 71 ppb.
Last updated: May 24, 2021