Ozone (O3) is a chemical compound found in the upper layer of our atmosphere, as well as close to the ground. In the upper layer of the atmosphere, ozone helps to protect life by protecting our planet from the sun’s ultra-violet rays, but ground-level ozone is considered a pollutant and can harm human and plant health.

The Forest Health Index looks only at ground-level ozone. Measurements are drawn from local air quality stations that measure ozone and other harmful pollutants.

What We're Seeing

Near average: Ozone levels have been near average for this watershed over the past five years. This means that the pollution levels are at or below health standards recommended by the EPA.

What We're Monitoring

By reacting with other chemicals, ozone can damage important tissues in both animals and plants. In humans, high ozone levels can cause throat irritation or trouble breathing. In plants, it can cause damage to leaves, prevent growth, or make plants more susceptible to diseases and insect infestations. Aspen trees, in particular, seem to be susceptible to damage from ozone.

Future Outlook

Ground-level ozone forms chemical compounds—either nitrogen oxides (NOx) or volatile organic compounds (VOCs)—in reaction to in sunlight. These reactions occur most readily on warm days. NOx and VOCs are produced from pollution from motor vehicles, burning fuels in industrial production, and use of some chemical solvents. As human populations grow, ozone levels may grow also unless steps are taken to prevent pollution. Ozone pollution can be reduced by turning off cars instead of idling them or by powering our cars, homes, and industries using energy that does not come from burning fossil fuels.