Carbon Monoxide

Houston Levels of Carbon Monoxide Remain Well Below EPA’s Health Based Standard

What is Carbon Monoxide?

Carbon monoxide (CO) is a colorless, odorless gas that is a by-product of combustion.  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.

Where is CO Found?

Nationally and especially in urban areas, the majority of outdoor CO is emitted by mobile sources such as cars, trucks, and construction equipment.
EPA first set health-based standards for CO in 1971.  Because CO can have different effects over longer and shorter-term time periods, EPA set an 8-hour standard at 9 parts per million (ppm) and a 1-hour standard at 35 ppm.
Every urban area in the country has air quality that meets the current CO standards. Most sites have had measured concentrations below the national standards since the early 1990s because improvements in motor vehicle emissions controls contributed to significant reductions in outdoor concentrations.

Carbon monoxide is still considered a very significant indoor air pollutant. CO can build up to unsafe, even deadly levels due to leaks in furnaces and gas generators. EPA provides a great deal of information on how to protect yourself and your family from indoor CO pollution at:

Houston’s levels of outdoor CO pollution are far below the national health based standards. The charts below show the two CO standards, and levels reported at the highest monitor in Houston.

For more information on Carbon Monoxide, please visit:

Houston CO Levels 2011 – 2015