(CO) is a colorless, odorless, and tasteless gas, that is formed
whenever carbon in fuel is not burned completely. It is a component
of motor vehicle exhaust, which contributes to about 56% of all
emissions. It may temporarily
accumulate at harmful levels, especially in calm weather during
winter and early spring, when fuel combustion reaches a peak and
carbon monoxide is chemically most stable due to the low
Sources of carbon monoxide include:
- Automobile emissions. (High levels
are possible near large parking lots, traffic jams, or crowded
city streets, where large numbers of slow-moving cars accumulate.)
In cities, 85-95% of all CO emission may come from motor vehicle
- Home/building heating.
- Volcanoes, thunderstorms and
- Vegetation during various growth
- The chemical transformation of
methane, a gas emitted from decaying plants in swamps and
Carbon monoxide from natural sources
usually dissipates quickly over a large area, posing no threat to
enters the blood stream by combining with hemoglobin, the substance
that carries oxygen to the cells. This combination occurs 200 times
more readily with carbon monoxide than with oxygen, starving the
body of oxygen. Carbon monoxide adversely impacts health in many ways:
- It affects the central nervous
system at relatively low concentrations.
- It weakens heart contractions,
lowering the volume of blood distributed to various parts of the
- It significantly reduces a healthy
person's ability to perform manual tasks, such as working, jogging
- It causes healthy people to feel
tired and drowsy from short-term exposure to concentrations
greater than 30 parts per million (ppm).
- It causes shortness of breath and
chest pain in people with heart disease at exposures as low as 10
- It induces irritability,
headaches, rapid breathing, blurred vision, lack of coordination,
nausea, dizziness, confusion and impaired judgement in healthy
people at levels greater than 35 ppm.
Even three or four hours after
exposure, half the excess carbon monoxide may remain in the blood
People especially susceptible to CO
- Children (and the human fetus).
- The elderly.
- Those with respiratory or heart
illnesses. (The 4.2 million people in the U.S. suffering from
angina pectoris - a disease characterized by brief spasmodic
attacks of chest pain due to insufficient oxygen levels in the
heart muscles - are especially susceptible.)
- Those with anemia.
- Those exposed for long periods of
time, such as traffic officers and people sitting in parked/idling
cars over sustained periods.
- Cigarette smokers. (Smoking while
driving in heavy traffic may result in increased exposure - from
cigarette smoke and engine exhaust. Tests of automobile drivers
show exposure to high levels of carbon monoxide can impair a
driver's judgment and ability to respond rapidly in traffic. It
can also impair vision and produce headaches.)
However, at high concentrations, CO
is poisonous to everyone, even healthy people.
At concentrations commonly monitored
in the ambient air, carbon monoxide does not appear to adversely
affect plants, wildlife, or materials.
contribute to the formation of smog, ground-level
Carbon monoxide is a common indoor
air contaminant. Concentrations of 1 to 2 ppm are common in homes
with normal gas-fired furnaces; malfunctioning furnaces can lead to
indoor concentrations of more than 120 ppm.