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Carbon Monoxide
What is Carbon
Monoxide?
Health Effects
National Ambient Air Quality Standards
What is Carbon Monoxide?
Carbon monoxide (CO) is a colorless, odorless, poisonous gas formed when carbon in fuels is not burned completely. It is a byproduct of highway vehicle exhaust, which contributes about 60 percent of all CO emissions nationwide. In cities, automobile exhaust can cause as much as 95 percent of all CO emissions. These emissions can result in high concentrations of CO, particularly in local areas with heavy traffic congestion. Other sources of CO emissions include industrial processes and fuel combustion in sources such as boilers and incinerators.
Health Effects
When carbon monoxide enters the bloodstream, it reduces the delivery of oxygen to the body's organs and tissues. The health threat from exposure to CO is most serious for those who suffer from cardiovascular disease, particularly those with angina or peripheral vascular disease. Healthy individuals are also affected, but only at higher levels of exposure. Exposure to elevated CO levels can cause impairment of visual perception, manual dexterity, learning ability and performance of complex tasks.
National Ambient Air Quality Standards
The health-based National Ambient Air Quality Standard for carbon monoxide is 9 parts per million (ppm), measured as an 8-hour nonoverlapping average not to be exceeded more than once per year. The rounding convention in the standard specifies that values of 9.5 PPM, or greater, are counted as exceeding the level of the standard. An area meets the carbon monoxide NAAQS if no more than one 8-hour value per year exceeds the threshold. (High values that occur within 8 hours of the first one are exempted. This is known as using "nonoverlapping averages.") To be in attainment, an area must meet the NAAQS for two consecutive years and carry out air quality monitoring during the entire time. All areas in Region 5 are attaining the NAAQS for carbon monoxide.