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Air Pollution and Public Health in Utah

Carbon Monoxide (CO)
Sources | Health Effects | Reduce Exposure | Standards and Trends | Data and Indicators

Carbon monoxide (CO), one of the EPA criteria pollutants, is a colorless, odorless, tasteless, non-irritating gas found in both indoor and outdoor air. It is formed when carbon-based fuel (e.g., gasoline, oil, wood, coal, etc.) is not burned completely (ATSDR, 2012b). CO can come from both human-made as well as natural sources. When released into the air, CO remains for an average of two months. Eventually, it reacts with other atmospheric compounds and is converted to carbon dioxide. Microorganisms in the soil and water can also convert CO to carbon dioxide (ATSDR, 2012a).



Sources | Top

The vast majority of human-related CO emissions, particularly in urban areas, come from gasoline-powered automobile exhaust, although the amount of CO released from this source has declined significantly over the past several decades due to more effective emission control equipment (ATSDR, 2012a). Petroleum refineries, gas and coal burning power plants, and petroleum-based chemical plants also release CO into the atmosphere. Natural sources of CO include volcanic activity, wildfires, and releases from vegetation as a metabolic byproduct. Indoor sources of CO are typically man-made and include improperly installed or filtered kerosene and gas space heaters, furnaces, wood stoves, and generators. Exposure to CO may also occur from cigarette smoke, both in smokers and those exposed to second-hand smoke (ATSDR, 2012a).

Figure 1: 2014 CO emissions in Utah by source sector


In 2014, 53% of CO emissions in Utah came from mobile sources (e.g., motor vehicles) (Figure 1). Releases from soil and vegetation (also known as biogenic sources) were the second largest source of CO emissions. A county level distribution of CO emissions is shown in Figure 2 (note that emission levels do not indicate air quality) (EPA, 2016c).

Figure 2: 2014 Utah CO emissions by county (tons per square mile)

2014 Utah carbon monoxide emissions by county

Figure courtesy of EPA



Health Effects | Top

Carbon monoxide breathed in from the atmosphere rapidly enters all parts of the body, including the blood, brain, heart, and muscles. CO in the body is removed through your lungs when you breathe, which takes approximately one day (ATSDR, 2012a). Exposure to high levels of CO can be life threatening, and CO poisoning is the leading cause of death due to poisoning in the U.S. (ATSDR, 2012b). Normally, red blood cells transport oxygen to, and carbon dioxide from, all tissues in the body. However, red blood cells bind more strongly to CO than to oxygen, thus reducing the oxygen carrying capacity of the blood. This can lead to a lack of an adequate oxygen supply to tissues (a condition known as hypoxia). Headache, nausea, vomiting, dizziness, blurred vision, confusion, chest pain, difficulty breathing, and heart and brain damage have been reported in people inhaling CO (ATSDR, 2012b).

People with existing heart or lung diseases are often more vulnerable to the toxic effects of CO, particularly during physical exertion when more oxygen than normal is needed. During pregnancy, breathing high levels of CO can cause miscarriage and other adverse birth outcomes, and breathing lower levels may harm the mental development of the child (ATSDR, 2012a; EPA, 2013m).



Ways to Reduce Exposure | Top

Due to the substantial reductions in CO in outdoor air, the most dangerous levels of CO usually occur indoors. You can reduce the potential for CO exposure by making sure that appliances that burn natural gas, kerosene, wood, or other fuels (e.g., stoves, furnaces, water and space heaters, generators, etc.) are properly installed, vented, and maintained. Do not burn charcoal or use gas-powered tools indoors, as this can lead to dangerous levels of CO. Idling a vehicle in an enclosed space like a closed garage can allow CO to build up quickly and should be avoided. Avoiding smoke from tobacco products can also reduce exposure to CO. Installing and maintaining CO detectors in homes and boats can alert you before dangerous levels of CO accumulate; it is important to note that most smoke detectors do not detect CO.



Standards and Trends | Top

The primary National Ambient Air Quality Standard (NAAQS) for CO is 9 parts per million (ppm), based on an eight hour average. This standard was originally set by the first Clean Air Act in 1971 and has been retained through the present day (EPA, 2013c). Everywhere in the country has air quality that meets the CO standard, and most sites have measured decreasing concentrations below the NAAQS since the early 1990s (Figure 3).

Figure 3: Average national CO concentration, 1980 – 2015

Average national carbon monoxide concentration, 1980 - 2012

Figure courtesy of EPA | How to interpret this graph


The same trend can be seen when examining the Southwest region states of Arizona, Colorado, New Mexico, and Utah (Figure 4), as well as data from twelve CO monitors along the Wasatch Front (Figure 5).

Figure 4: Average CO concentration in the Southwest, 2000 – 2015

Average carbon monoxide concentration in the Southwest region, 2000 - 2012

Figure courtesy of EPA | How to interpret this graph


Figure 5: Average CO concentration along the Wasatch Front, 2000 – 2014


There have been no violations of the carbon monoxide NAAQS in Utah since 1993. Salt Lake City, Ogden, and Provo were officially re-designated to attainment status for CO in 1999, 2001, and 2006, respectively (UDAQ, 2014a). Figure 6 shows the current CO maintenance areas in Utah.

Figure 6: CO maintenance areas in Utah

Carbon monoxide maintenance areas in Utah

Figure courtesy of UDAQ



Data and Indicators | Top

The Utah Environmental Public Health Tracking Program (EPHT) has created a number of indicators exploring data on carbon monoxide in Utah. An indicator is a fact or trend that indicates the level or condition of something. Well known indicators include gross national product, unemployment rates, and presidential approval ratings. In a public health context, indicators show trends like cancer rates, drinking water contamination levels, and blood lead levels in children. Visit the EPHT frequently asked questions page for more information.

Carbon Monoxide Indicators