Carbon monoxide (CO) is a colorless, odorless, and poisonous gas and one of six criteria pollutants for which EPA has established protective standards. CO forms when the carbon in fuels does not completely burn. Vehicle exhaust contributes roughly 60% of all CO emissions nationwide and up to 95% in cities. Other sources include fuel combustion in industrial processes and natural sources such as wildfires. CO concentrations typically are highest during cold weather because cold temperatures make combustion less complete and cause inversions that trap pollutants low to the ground.
Health Impacts of Exposure
CO enters the bloodstream through the lungs and binds chemically to hemoglobin, the substance in blood that carries oxygen to cells. In this way, CO interferes with the ability of the blood to transport oxygen to organs and tissue throughout the body. This can cause slower reflexes, confusion, and drowsiness. It can also reduce visual perception and coordination and decrease the ability to learn. People with cardiovascular disease, such as angina, are most at risk from exposure to CO. These individuals may experience chest pain and more cardiovascular symptoms if they are exposed to CO, particularly while exercising.