The State of the Air report released Wednesday gives King County an F grade and Pierce County a C grade in ozone pollution.

King County had 11 high ozone days and Pierce County had less than half that number.

The information on Snohomish County was incomplete.

For fine particle pollution, Pierce and Snohomish counties got F's, while King and Spokane counties got C's.

Particle pollution goes up when high temperatures "cook" pollutants in the air into a hazy, ozone-heavy mix. Traffic is a key contributor.

Bakersfield, California is the most particle-polluted city.

Dr. Al Brady of the American Lung Association of the Northwest says the report doesn't account for tighter standards to reduce diesel emissions and replace smoky wood stoves in the region.

No Washington cities made the list of the worst 25 in either category.

The national report based its rankings on air quality measurements that local and state agencies reported to the U.S. Environmental Protection Agency between 2005 and 2007.