Carbon monoxide is a colorless, odorless, and (at much higher
levels) poisonous gas, formed when carbon in fuels is not burned
completely. It is a product of motor vehicle exhaust, which contributes
about 60 percent of all CO emissions nationwide. High concentrations
of CO generally occur in areas with heavy traffic congestion. In
cities, as much as 95 percent of all CO emissions may emanate from
automobile exhaust. Other sources of CO emissions include industrial
processes such as carbon black manufacturing, non-transportation
fuel combustion, and natural sources such as wildfires. Woodstoves,
cooking, cigarette smoke, and space heating are sources of CO in
indoor environments. Peak CO concentrations typically occur during
the colder months of the year when CO automotive emissions are greater
and nighttime inversion conditions are more frequent. |
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