State of Smog in the Western United States

In August, the U.S. Environmental Protection Agency (EPA) posted updated data showing the air quality status of counties throughout the United States.  We assessed the status of counties in the American West in terms of compliance with ambient air quality standards for ozone.  Ozone forms when air pollution from smokestacks, tailpipes, and oil and gas fracking operations reacts with sunlight.  It’s the key ingredient of smog and can be a serious health threat.

The current standard is limits concentrations over an eight-hour period to no more than 0.075 parts per million, an extremely low amount that reflects how poisonous ozone gas can be.  However, science advisors to the EPA recently recommended the agency lower the standard to a level below 0.070 parts per million to as low as 0.060 parts per million to ensure adequate protection of public health.

A violation of the ozone ambient air quality standards occurs when the three-year average of the annual fourth highest maximum reading is higher than the standard.  This average is called the “design value.”  Areas with a design value above the standard have consistently high ozone.  Areas with a design value below the standard may still have air quality that exceeds the standards at times and puts public health at risk, but not on a consistent basis.

We mapped out areas in the American West with design values above the current ambient air quality standard of 0.075 ppm, a standard of 0.070, a standard of 0.065, and a standard of 0.060.  The map is a surprising sign that clean air in the west is under immense risk.

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