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Sulfur oxides (SOx) are colorless gases that are the result of burning sulfur. All fuels used by man (oil, coal, natural gas, wood, etc.) contain some sulfur, and during the combustion process, sulfur reacts with oxygen to form SOx. The primary source of sulfur oxides is the burning of these fossil fuels, particularly coal, at industrial facilities. Sulfur dioxide(SO2) is used as an indicator of all SOx concentrations in the ambient air, because it is the most easily measured. The National Ambient Air Quality Standards ( NAAQS) for SO2 are 0.03 ppm on an annual average and 0.14 ppm for a 24-hour average. There is also a secondary standard (not based on human health) with a 3-hour averaging period (0.5 ppm.) It allows only one exceedance of the standard per year.
Sulfur dioxide is known to irritate the respiratory system. SO2 is particularly detrimental to individuals who suffer from respiratory diseases such as asthma and chronic bronchitis. SO2 can also combine with particles and moisture in the air creating an even greater health risk. It contributes to the formation of acid rain by transforming into sulfuric acid in the atmosphere. Acid rain can damage lakes and aquatic life, building materials, and plant life.
Sulfur dioxide emissions from combustion at power plants are controlled by "scrubbing" the gas leaving the plant or by removing sulfur from the fuel before it is burned. Individuals can reduce SO2 emissions by limiting the use of electricity, by turning off electric devices not in use, and by making use of more efficient electric devices (lights, refrigerators, motors, etc.) and alternate energy sources. Emissions of SO2 in nonattainment areas by source are shown in Figure 5.
In 1978, the EPA designated Salt Lake and Tooele Counties as a nonattainment area for SO2 based on ambient data collected at air monitoring locations in Magna and Tooele. In 1981, the EPA removed the nonattainment status for all of Tooele County except the eastern portion above 5,600 feet. Later in 1981, the State submitted an implementation plan (SIP) to the EPA that addressed the SO2 violations. The primary control measure was replacement of Kennecott Copper Corporation's reverberatory smelter with a new and cleaner Noranda smelter. The EPA approved the State's SIP in 1994, and no violations of the standard have been recorded since the new smelter and the "tall stack" were constructed. In 2005, Utah requested that EPA redesignate the area to attainment.
SO2 concentrations are not a function of meteorology to the same extent as CO, PM10 and ozone. Therefore, we do not typically compare SO2 to any meteorological parameter. SO2 concentrations have decreased dramatically over the past eight years due to major SO2 controls at industrial facilities in the area. Most notably, Kennecott's Flash Smelting Process came on line in June 1995 and made a significant difference in SO2 concentrations in the Wasatch Front region.
Sulfur dioxide tends to be a localized problem and therefore the network locates a monitor near the largest sources of SO2. The maximum values of SO2 have been far below the NAAQS for the past 25 years.