Ground level ozone in Washington's air

We monitor ozone levels at 13 locations to protect your health and the environment. Currently, all areas of Washington meet the ozone air quality standard. The Tri-Cities area is being closely monitored because recent samples near Kennewick detected periods of relatively high ozone levels.

Click image to enlarge.


Ozone high in the Earth's atmosphere protects us from the sun's harmful radiation. But at ground level, ozone is an air pollutant that harms people and plants. Ground-level ozone forms when nitrogen oxides and volatile organic compounds react with each other in sunlight and hot temperatures. This pollution comes from vehicles, industry, and other sources and contributes to smog formation.

Ecology and local clean air agencies monitor air to ensure ground-level ozone meets Washington's air quality standards. Ozone levels used to exceed national standards in the Seattle and Vancouver areas. Due to improvements in vehicles and other emission-reducing requirements, ozone pollution has declined even as the population continues to grow.

Ozone in Washington

In the late 1970s and '80s, ozone levels downwind of some of Washington's urban areas were high enough to violate national standards. Parts of Snohomish, King, Pierce, and Clark counties failed to meet the ozone standard because air pollutant emissions from these areas contributed to high ozone levels.

By the mid-90s, all of Washington was meeting the national standard. More stringent emissions standards for vehicles, cleaner fuels, and gas station vapor controls helped reduce ozone pollution.

Generally, ozone levels tend to be higher downwind of urban areas. This is because it takes a while for pollutants to react with sunlight. Although the state currently meets the ozone standards, we continue to watch the following areas closely:

Ecology and local clean air agencies monitor air pollution throughout the state. This map illustrates areas of concern we are monitoring closely. 

Maintaining clean air

To make sure air continues to meet Washington standards, we partner with local clean air agencies to monitor ozone at 13 locations. We monitor ozone at:

  • Urban locations (Seattle, Vancouver, and Spokane)
  • Downwind of urban locations (eight sites)
  • Natural rural location (Olympic Peninsula)
  • High elevation location (Mt. Rainier)

What you can do

To help prevent ozone from forming on hot days:

  • Don't drive unless you have to. Share a ride, take the bus, ride your bike, or walk when you can. If you must drive, combine your trips.
  • Refuel your car or truck after dusk. Don't top off your tank.
  • Limit engine idling.
  • Put off using gasoline-powered lawn and garden equipment until the hot spell is over.
  • Don't use your barbecue or fire pit.
  • Conserve electricity. Set your air conditioner at a higher temperature.
  • Save that painting project for later. Don't use paint or other products that release solvent gases.

When pollution rises on hot days:

  • Cut down on strenuous physical activity outside.
  • Stay inside until it cools down outside.
Environmental effects

Ozone damages trees and plants. It impairs plant growth, and makes them more easily harmed by insects and disease.

Health effects