Information about Carbon Monoxide (CO)
Condensed from Measuring Air Quality: The Pollutant Standards Index;
Office of Air Quality Planning and Standards, US EPA; EPA 451/K-94-001;
February 1994.
Sources
Carbon Monoxide (CO) is an odorless, colorless gas that is
a by-product of the incomplete burning of fuels. Industrial processes
contribute to CO pollution levels, but the principal source of CO
pollution in most large urban areas is the automobile. Cigarettes and
other sources of incomplete burning in the indoor environment also
produce CO. CO is inhaled and enters the blood stream; there it binds
chemically to hemoglobin, the substance that carries oxygen to the
cells, thereby reducing the amount of oxygen delivered to all tissues
of the body. The percentage of hemoglobin inactivated by CO
depends on the amount of air breathed, the concentration of CO in air,
and length of exposure; this is indexed by the percentage of
carboxyhemoglobin found in the blood.
Health effects
CO weakens the contractions of the heart, thus
reducing the amount of blood pumped to various parts of the body
and, therefore, the oxygen available to the muscles and various
organs. In a healthy person, this effect significantly reduces the ability
to perform physical exercises. In persons with chronic heart diseases,
these effects can threaten the overall quality of life, since their systems
are unable to compensate for the decrease in oxygen. CO pollution is
also likely to cause such individuals to experience angina during
exercise. Adverse effects have also been observed in individuals with
heart conditions who are exposed to CO pollution in heavy freeway
traffic for 1 to 2 hours or more.
In addition, fetuses, young infants, pregnant women, elderly people,
and individuals with anemia or emphysema are likely to be more
susceptible to the effects of CO. For these individuals, the effects are
more pronounced when exposure takes place at high altitude
locations, where oxygen concentration is lower. CO can also affect
mental function, visual activity, and alertness of healthy individuals,
even at relatively low concentrations.
Air quality levels
The air quality standard for CO, which is designed
to protect public health with an adequate margin of safety, is 9 parts
per million, averaged over 8 hours. EPA is required to issue a public
alert when CO levels reach 15 ppm, a public warning when CO levels
reach 30 ppm, and a public declaration of emergency at the level of 40
ppm. The significant harm level, at which serious and widespread
health effects occur to the general population, is 50 ppm of CO.
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