Jump to main content or area navigation.

Contact Us

Carbon Monoxide


August 15, 2011 - EPA finalizes National Ambient Air Quality Standards for carbon monoxide
Learn More

February 16, 2011 - EPA will hold public hearing on proposal for the carbon monoxide standard.
Learn More

January 28, 2011 - EPA Proposed Action on National Air Quality Standards for Carbon Monoxide
Learn More

Carbon monoxide (CO) is a colorless, odorless gas emitted from combustion processes.  Nationally and, 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 a 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 1994 and the Agency chose not to revise the standards at that time.

For more information about CO:

Basic Information - Basics about CO air pollution.

Health - Effects of CO air pollution.

CO Standards - Links to technical information related to setting the national air quality standards for CO to protect public health.

Regulatory Actions - Links to proposed and final rules, fact sheets, and other rulemaking documents.

Air Quality Trends - Progress made in reducing CO in the air.

Air Emission Sources - Summarizes CO air emissions by source at national, state and local levels.


Jump to main content.