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Health Effects of Pollution Trapped in Inversions
Inversions occur during winter months when normal conditions (cool air above, warm air below) are inverted. Inversions trap a dense layer of cold air under a layer of warm air. They act much like a lid, trapping pollutants within the cold air near the valley floor. The Wasatch Front valleys and their surrounding mountains act much like a pot, holding the air in the valleys. The longer the inversion lasts, the stronger the pollutants concentrate within it. Visibility often deteriorates well in advance of harmful concentrations of pollutants.
Meteorological events, such as high-pressure systems over Utah and stagnant air, cause inversions.
Higher concentrations of pollution usually require more than just a high-pressure inversion. Inversions can be extended for many days when snow covers the valley floors and reflects sunlight needed to break the inversion. This allows pollution to continue to concentrate near ground level. Pollution also increases when fog is present to facilitate chemical reactions that create even more particles.
The primary winter pollutant is particulate matter (PM). Soot, dust, and emissions from vehicles are components of particulate.
Very fine particles are the main concern. Particulate size is measured in microns. PM10 is particulate matter of any kind measuring 10 microns or less in diameter They are one-tenth the diameter of a human hair. PM2.5 is particulate matter measuring 2.5 microns or less in diameter.
The Division of Air Quality (DAQ) issues a health advisory for sensitive individuals based on the amount of PM2.5 in the air. That pollution level also triggers a “red,” “yellow,” or “green” wood-burning designation. (See also the fact sheet on Utah’s Winter Air Quality Program: “Red Light, Green Light.”) DAQ issues a health advisory for sensitive individuals and a “yellow-burn” condition at 40 ug/m3—well below the health standard of 65 ug/m3 for PM2.5. A “red-burn” condition is triggered before the health standard is exceeded, and the health advisory for sensitive individuals continues.
Another pollutant is carbon monoxide ¾ a colorless, odorless gas. When the carbon in fuel is not burned completely, it forms carbon monoxide. It is a component of motor vehicle exhaust, and in areas with heavy traffic congestion, high levels of carbon monoxide are often present. The health standard for carbon monoxide is 9 parts per million for an 8-hour average.
The third major pollutant in inversion situations is sulfur dioxide. When fuel (mainly coal and oil) is burned, or during metal smelting and other industrial processes, sulfur dioxide is formed. The health standard for sulfur dioxide is .14 parts per million for a 24-hour average.
Along the Wasatch Front, 60 percent of particulate matter and 70 percent of carbon monoxide emissions come from vehicles. Industrial sources account for 70 percent of sulfur dioxide emissions, with vehicles accounting for the remaining 30 percent.
Particulate matter, carbon monoxide, and sulfur dioxide affect breathing and respiratory function. Existing respiratory and cardiovascular disease may be aggravated, the body’s defense system against bacteria and viruses may be altered, and lung tissue may be damaged. Some studies indicate that particulate matter decreases the heart’s ability to respond to physical stress. When the heart cannot adapt well to changes in the heart rate, its oxygen-carrying capacity in the blood is reduced.
When carbon monoxide enters the bloodstream, it too reduces the delivery of oxygen to the body’s organs and tissues.
Health threats are most serious for those who suffer from cardiovascular disease, asthma, emphysema, influenza, and bronchitis. Children and the elderly are also likely to be adversely affected by heavy concentrations of these pollutants.
The Utah Division of Air Quality issues health advisories whenever pollution increases to levels of concern as determined by U.S. Environmental Protection Agency criteria. Health advisories are most critical for people with respiratory and heart diseases, the elderly, and children. When a health advisory is issued, they should limit outdoor exertion whenever possible.
- Division of Air Quality Website
- Hotline for Salt Lake and Davis Counties: 801-536-0072
- Hotline for Weber, Utah, and Cache Counties: 1-800-228-5434
- Local Newspapers and Television Stations