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Air Quality Program

Carbon Monoxide (CO)

Carbon Monoxide is an odorless, tasteless, colorless gas emitted by any form of combustion. Common sources include:

  • Motor vehicles
  • Wood stoves and fireplaces
  • Outdoor burning
  • Industrial combustion

Health Effects

It deprives the body of oxygen by reducing the blood’s capacity to carry oxygen. It can cause headaches, dizziness, nausea, listlessness. In high doses, it may cause death.

National Ambient Air Quality Standards (NAAQS) for Carbon Monoxide

Identical primary (to protect health) and secondary (to protect public welfare) NAAQS for carbon monoxide were set in 1971 at 9 ppm, 8-hour average, and at 35 ppm, 1-hour average, neither to be exceeded more than once a year. In Washington, parts of Seattle, Tacoma, Vancouver, Spokane, and Yakima were designated nonattainment for the 1971 carbon monoxide standard. The areas met the standard and were redesignated attainment between 1996 and 2004. In 1985, EPA decided not to revise the primary carbon monoxide standard and revoked the secondary standard.

After the most recent review of the carbon monoxide standard, EPA proposed to retain the current primary standards. After review of the air quality criteria, EPA concluded that no secondary standard should be set for carbon monoxide. EPA is also making changes to the ambient air monitoring requirements for carbon monoxide, including those related to network design, and is updating aspects of the federal reference method.

Technical Table

Pollutant Averaging Time Level Remarks Measurement Method Interpretation Method
Carbon Monoxide 8-hour 9 ppmv Not to be exceeded more than once per year 40 C.F.R. Part 50, Appendix C WAC 173-476-160(3)
1-hour 35 ppmv

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