Ozone Standard Exceedances in National Parks

At ground level, ozone is harmful to human health and the environment.

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 so far in 2018 along with ozone season summaries for 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.

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.

Download 2018 data in a tabular format
Download NPS ozone exceedance data from 2008–2017

Last updated: September 11, 2018

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