Sulfur dioxide in Washington's air

Sulfur dioxide

Sulfur dioxide (SO₂) is a colorless gas with a strong smell. It gets into the air when fuel that contains sulfur is burned. Major sources in Washington are:

• Industrial facilities such as fossil fuel power plants, aluminum smelters, oil refineries, and pulp mills
• Ships and locomotives

EPA set National Ambient Air Quality Standards (NAAQS) for sulfur dioxide, which specify levels of the pollutant in outdoor air that can impact public health or harm the environment. There are two current standards:

• 1-hour sulfur dioxide standard (health-based)
• 3-hour sulfur dioxide standard (welfare-based)

Sulfur dioxide in Washington

Thanks to improved pollution controls on industrial facilities and cleaner transportation fuels, Washington's sulfur dioxide levels have declined dramatically in recent decades.

After EPA's adoption of a new sulfur dioxide standard in 2010, we evaluated sulfur dioxide levels in all 39 counties in Washington. We found that, except for a small area near an aluminum smelter in Whatcom County, the rest of Washington complies with the standard. Learn more about our findings on sulfur dioxide levels in the air.

Maintaining clean air

We monitor sulfur dioxide at six locations:

• One location in Seattle, representing urban conditions and trends.
• One location on the Olympic Peninsula representing rural background (or natural) conditions.
• One location in Anacortes, representing neighborhood conditions near an industrial region.
• Two locations near Alcoa Intalco Works near Ferndale in Whatcom County to evaluate the area’s compliance with the 2010 1-hour sulfur dioxide standard.
• One location near Alcoa Wenatchee, close to Malaga in Chelan County and on the border of Douglas County, to evaluate the area’s compliance with the 2010 standard.

What you can do

There are some things you can do to protect yourself from sulfur dioxide. You can:

• Limit outdoor activities during times of high air pollution.
• Close windows and vents during periods of high air pollution.
• Consult with your health care provider about a personal mask and air purification device.