Carbon monoxide is a colorless, ordorless gas emitted by motor vehicles as a result of incomplete combustion of fossil fuels. This occurs when carbon or substances that contain carbon are not burned completely, such as gasoline, wood or coal.
Emissions primarily occur from motor vehicle exhausts -- by automobiles, buses and trucks -- and some industrial processes. Carbon monoxide is found in high concentrations along the roadside, especially where there is heavy traffic. Other areas might include parking garages and poorly ventilated tunnels.
A poisonous gas that replaces oxygen in the blood, carbon monoxide can affect the cardiovascular and nervous systems. It enters the blood via the lungs and permanently binds to hemoglobin (the iron-containing protein in red blood cells), preventing hemoglobin from carrying oxygen. Lower concentrations of CO have been shown to affect people with heart disease such as angina, can cause dizziness, headaches and fatigue, and at high concentrations, even death.
The U.S. Environmental Protection Agency sets National Ambient Air Quality Standards to protect public health. The limits for carbon monoxide are set at:
- 1-hour average: 35 parts per million
- 8-hour average: 9 parts per million