CO: What is it? Where does it come from?
Carbon monoxide, or CO, is a colorless, odorless gas that
is formed when carbon in fuel is not burned completely. It is a component
of motor vehicle exhaust, which contributes about 56 percent of all CO
emissions nationwide. Other non-road engines and vehicles (such as
construction equipment and boats) contribute about 22 percent of all CO
emissions nationwide. Higher levels of CO generally occur in areas
with heavy traffic congestion. In cities, 85 to 95 percent of all
CO emissions may come from motor vehicle exhaust. Other sources
of CO emissions include industrial processes (such as metals processing
and chemical manufacturing), residential wood burning, and natural sources
such as forest fires. Woodstoves, gas stoves, cigarette smoke, and
unvented gas and kerosene space heaters are sources of CO indoors.
The highest levels of CO in the outside air typically occur during the
colder months of the year when inversion conditions are more frequent.
The air pollution becomes trapped near the ground beneath a layer of warm
air.
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