Background on four emissions


    Over the next decade, power plant operators will face new requirements to make substantial reductions in emissions of sulfur dioxide (SO2 ) and nitrogen oxides (NOx ) beyond the levels called for in the Clean Air Act Amendments of 1999.

    They could also face requirements to reduce carbon dioxide (CO2 ) and mercury emissions. Several proposed bills in Congress have targeted reductions of these four emissions. At present, neither the future reduction requirement nor the complete timetable is known for any of these airborne emissions, which makes planning for compliance difficult.


Sulfur dioxide (SO2)

    Sulfur dioxide belongs to the family of sulfur oxide gases. These gases are formed when fuel containing sulfur (mainly coal and oil) is burned and during metal smelting and other industrial processes.

    The highest monitored concentrations of SO2 are recorded in the vicinity of large industrial facilities. Fuel combustion, accounts for most of the total SO2 emissions.

    SO2 emissions decreased 31 percent from 1981 to 2000 and 24 percent from 1991 2000.Reductions in SO2 concentrations and emissions since 1994 are due, in large part, to controls implemented under EPA s Acid Rain Program beginning in 1995.


Nitrogen Oxides (NOx)

    Nitrogen dioxide (NO2 )is a reddish brown, highly reactive gas that is formed in the ambient air through the oxidation of nitric oxide (NO).

    Nitrogen oxides (NOx), the term used to describe the sum of NO, NO2 and other oxides of nitrogen, play a major role in the formation of ozone, particulate matter, haze and acid rain.

    The major sources of man-made NOx emissions are high-temperature combustion processes, such as those occurring in automobiles and power plants. Home heaters and gas stoves also produce substantial amounts of NO2 in indoor settings.


Mercury (From the DOE website. For full text click here)

    Mercury exists in trace amounts in coal, waste and other materials. When these materials burn, mercury gases are released into the air. The amount of mercury being deposited today on land and in water is  much lower than in recent decades. Mercury deposition, at its highest in the 1950s, fell by more than half by the 1980s.

    Mercury emissions continued to fall in the decade of the 1990s. In 1993, U.S. yearly emissions totaled about 242 tons. By the end of the decade, emissions had declined to less than 160 tons per year. About 50 tons of mercury emissions come from power plants, about 1/3 of the total.


Carbon dioxide

     Carbon dioxide (CO2) is a colorless, odorless gas that humans breath out and plants breath in during respiration. Although carbon dioxide emissions are not harmful to health, they have a warming effect on the atmosphere. This warming, along with a natural rise in temperature is referred to as "global warming." Carbon dioxide, methane, particulate matter (especially black carbon or soot), nitrous oxide, fluorinated compounds, and ozone, are some of the compounds contributing to global warming. Carbon dioxide emissions are largely due to the combustion of fossil fuels in electric power generation, motor vehicles, and industry.


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