What is Carbon Monoxide?

advantages and disadvantages of cash budget Carbon monoxide (CO) is a colorless, odorless, poisonous gas. A product of incomplete burning of hydrocarbon-based fuels, carbon monoxide consists of a carbon atom and an oxygen atom linked together.

Why is Carbon Monoxide a Public Health Problem?

Carbon monoxide enters the bloodstream through the lungs and forms carboxyhemoglobin, a compound that inhibits the blood’s capacity to carry oxygen to organs and tissues. Persons with heart disease are especially sensitive to carbon monoxide poisoning and may experience chest pain if they breathe the gas while exercising. Infants, elderly persons, and individuals with respiratory diseases are also particularly sensitive. Carbon monoxide can affect healthy individuals, impairing exercise capacity, visual perception, manual dexterity, learning functions, and ability to perform complex tasks.

In 1990, 42 urban areas in the United States exceeded the Environmental Protection Agency’s (EPA’s) National Ambient Air Quality Standard for carbon monoxide. Approximately 22 million people live in these areas.

How is Carbon Monoxide Formed?

Carbon monoxide results from incomplete combustion of fuel and is emitted directly from the tailpipe. Incomplete combustion is most likely to occur at low air-to-fuel ratios in the engine. These conditions are most common during vehicle starting when air supply is restricted (“choke”); when cars are not tuned properly; and at altitude, where “thin” air effectively reduces the amount of oxygen available for combustion (except in cars that are designed or adjusted to compensate for altitude).

Nationwide, two-thirds of the carbon monoxide emissions come from transportation sources, with the largest contribution coming from highway motor vehicles. In urban areas, the motor vehicle contribution to carbon monoxide pollution can exceed 90%.

What’s Been Done to Control Carbon Monoxide Levels?

The Clean Air Act gives state and local governments primary responsibility for regulating pollution from power plants, factories, and other “stationary sources.” EPA has primary responsibility for “mobile source” pollution control.

The EPA motor vehicle program has achieved considerable success in reducing carbon monoxide emissions. EPA standards in the early 1970s prompted auto makers to improve basic engine design. By 1975, most new
cars were equipped with catalytic converters designed to convert carbon monoxide to carbon dioxide. Catalysts typically reduce carbon monoxide emissions upwards of 80%. In the early 1980s, auto makers introduced more sophisticated converters, plus on-board computers and oxygen sensors to help optimize the efficiency of the catalytic converter.

Passenger cars coming off today’s production lines are capable of emitting 90% less carbon monoxide over their lifetimes than their uncontrolled counterparts of the 1960s. As a result, ambient carbon monoxide levels have dropped, despite large increases in the number of vehicles on the road and the number of miles they travel. With continued increases in vehicle travel, however, carbon monoxide levels will eventually begin to climb again unless even more effective emission controls are employed.

What More Can Be Done?

Carbon monoxide emissions from automobiles increase dramatically in cold weather. This is because cars need more fuel to start at cold temperatures, and because some emission control devices (such as oxygen sensors and catalytic converters) operate less efficiently when they are cold.

Cars are currently tested for carbon monoxide emissions at 75°F. EPA recently finalized regulations that will also require cars to meet a carbon monoxide standard at 20°F. The new cold-temperature carbon monoxide standards take effect beginning with 1994 models of cars and light trucks.

The 1990 Clean Air Act also stipulates expanded requirements for Inspection and Maintenance programs. These routine emission system checks should help identify malfunctioning vehicles that emit excessive levels of carbon monoxide and other pollutants. In addition, EPA has proposed requirements for on-board warning devices to alert drivers when their emission control systems are not working properly.

Another strategy to reduce carbon monoxide emissions from motor vehicles is to add oxygen-containing compounds to gasoline. This has the effect of “leaning out” the air-to-fuel ratio, thereby promoting complete fuel combustion. The most common oxygen additives are alcohols or their derivatives. “gasohol,” for example, is an oxygenated blend that contains 10% ethanol.

Several Western U.S. cities have successfully employed wintertime oxygenated gasolines for many years. The 1990 Clean Air Act expands this concept and requires that oxygenated gasolines be used during the winter months in 39 metropolitan areas with high carbon monoxide levels (see list on reverse side of page). The program began with the winter of 1992-93.

Cities Participating in Wintertime Oxygenated Fuels Program*

Albuquerque, NM
Anchorage, AK
Baltimore, MD
Boston-Lawrence-Salem, MA-NH
Chico, CA
Cleveland-Akron-Lorain, OH
Colorado Springs, CO
Denver-Boulder, CO
Duluth, MN-WI
El Paso, TX
Provo-Orem, UT
Fairbanks, AK
Fort Collins-Loveland, CO
Fresno, CA
Grants Pass, OR
Greensboro-Winston Salem-High Point, NC
Hartford-New Britain-Middletown, CT
Klamath County, OR
Las Vegas, NV
Los Angeles-Anaheim-Riverside, CA
Medford, OR
Memphis, TN-AR-MS
Minneapolis-St-Paul, MN-WI
Missoula, MT
Modesto, CA
New York-N. New Jersey-Long Island, NY-NJ-CT
Philadelphia-Wilmington-Trenton, PA-NJ-DE-MD
Phoenix, AZ
Portland-Vancouver, OR-WA
Raleigh-Durham, NC
Reno, NV
Sacramento, CA
San Diego, CA
San Francisco-Oakland-San Jose, CA
Seattle-Tacoma, WA
Spokane, WA
Stockton, CA
Syracuse, NY
Washington, DC-MD-VA

* The 1990 Clean Air Act requires oxygenated fuels in designated CO nonattainment areas where mobile sources are a significant source of CO emissions.

For Further Information:

The EPA National Vehicle and Fuel Emissions Laboratory is the national center for research and policy related to mobile source pollution. For additional information, contact the lab at 2565 Plymouth Road, Ann Arbor, MI 48105, or call (313) 668-4333.

Source: US EPA

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Last Update – 30-Sep-97