The National Park Service (NPS) monitors ozone in parks around the country. From April–October the number of days in each park that exceed National Ambient Air Quality Standard for ozone are reported. 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 2018, 2017 and 2016. 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.