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Air Quality: EPA's Integrated Science Assessments (ISAs)

Carbon Monoxide

Click to download the final report of the Integrated Science Assessment for Carbon Monoxide (2010) (PDF) (593 pp, 29 MB)
(PDF, 593 pp, 29 MB,
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The Issue
Carbon monoxide (CO) is a colorless, odorless gas emitted from combustion processes. Nationally, particularly in urban areas, the majority of CO emissions to ambient air come from mobile sources. CO can cause harmful health effects by reducing oxygen delivery to the body's organs (like the heart and brain) and tissues. At extremely high levels, CO can cause death.

EPA first set air quality standards for CO in 1971. For protection of both public health and welfare, EPA set an 8-hour primary standard at 9 parts per million (ppm) and a 1-hour primary standard at 35 ppm.

In a review of the standards completed in 1985, EPA revoked the secondary standards (for public welfare) due to a lack of evidence of adverse effects on public welfare at or near ambient concentrations.

The last review of the CO NAAQS was completed in 2011, and the Agency chose not to revise the standards at that time.

EPA Action
EPA's Carbon Monoxide research efforts are focused on improving emissions estimates, determining health and ecological effects, and improving modeling capabilities.

The Clean Air Act requires EPA to periodically review the science for six major air pollutants, including CO. EPA's National Center for Environmental Assessment develops Integrated Science Assessments (ISAs) that summarize the science related to the health and ecological effects caused by these pollutants. The ISA for CO is a comprehensive review of the policy-relevant scientific literature published since the last National Ambient Air Quality (NAAQS) review. ISAs provide a critical part of the scientific basis for establishing the NAAQS. EPA released the Integrated Science Assessment for Carbon Monoxide in Jan 2010. [See the history of CO for more detailed information]

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