Carbon monoxide (CO) is a colorless, odorless, tasteless gas that is slightly lighter than air. It is the most abundant pollutant in urban atmospheres and is very stable, having an average lifetime of 2-4 months in the atmosphere.

The primary source of CO is incomplete combustion of fossil fuels used for transportation and heating. In Fort Collins, approximately 85% of the CO comes from motor vehicles and 10% comes from woodburning. Other sources include refuse and agricultural burning, natural forest fires, and by-products from some industrial sources. CO tends to build up when shallow cold air masses are trapped close to the ground by warmer air masses above and by the mountains to the west. These temperature inversions occur most commonly during fall and winter months.

Carbon monoxide pollution affects everyone. It affects the central nervous system by depriving the body of oxygen. CO enters the body through the lungs, where it is absorbed into the bloodstream. Hemoglobin in the blood combines much more readily with CO than with oxygen, thus the amount of oxygen delivered by the blood is reduced in the presence of CO. CO can cause headaches, fatigue, vision and judgment impairment, dizziness, and drowsiness. The severity of the effects depends on the concentration and duration of exposure. Carbon monoxide is of even greater concern at our high elevations where the air is thinner and has less oxygen.

Particularly at risk are people with heart or breathing disorders, the elderly, pregnant women and their unborn children, and anemic individuals. Concern also exists for healthy children because of their increased oxygen requirements that result from their higher metabolism rate.

The primary National Ambient Air Quality Standard (NAAQS) for CO are 9 ppm (parts per million) averaged over an eight hour period and 35 ppm averaged over a one hour period. The EPA allows no more than one exceedance of the standard per year for any given location. Subsequent exceedances constitute violations of the NAAQS.

Primary standards are designed to protect human health and secondary standards to protect human welfare. There are no secondary CO standards.

Carbon monoxide has been monitored in Fort Collins since 1980. Concentrations are reported in the Fort Collins Air Quality Trends Reports. The downward trend in CO is due mostly to new car emission standards as well as oxygenated fuels and Colorado's inspection and maintenance program.