Explore Air

Legislative and Regulatory Proposals for Reducing Pollution from Electricity Generation

Clearer Skies Ahead

On March 10, 2005, EPA issued the Clean Air Interstate Rule (CAIR). CAIR will permanently cap emissions of sulfur dioxide (SO2) and nitrogen oxides (NOX) from electric-generating stations in the eastern United States. CAIR achieves large reductions of SO2 and/or NOX emissions across 28 eastern states and the District of Columbia. When fully implemented, CAIR will reduce SO2 emissions in these states by over 70 percent and NOX emissions by over 60 percent from 2003 levels. In a separate but related action on March 15, EPA issued the final Clean Air Mercury Rule to permanently cap and reduce mercury emissions from coal-fired power plants across the country. When fully implemented, the mercury rule will reduce utility emissions of mercury from 48 tons a year to 15 tons, a reduction of nearly 70 percent. Together the Clean Air Mercury Rule and the Clean Air Interstate Rule create a multi-pollutant strategy to reduce emissions throughout the United States.

For more information, please visit EPA's Clean Air Interstate Rule web page and Mercury Rule web page.

EPA is also considering new approaches for addressing impacts of nitrogen oxides in clean air areas, including national parks and wilderness areas. On February 23, 2005, EPA proposed three options to meet the objectives of the Clean Air Act's Prevention of Significant Deterioration (PSD) program for nitrogen oxides (NOx). These options include:

  1. retaining the existing increments for NOx–measured as nitrogen dioxide (NO2) in the ambient air as established in October 1988;
  2. allowing states that choose to implement an interstate cap and trade program for sources of NOx to rely on the benefits of that program in place of the existing increments to prevent significant deterioration of NOx air quality; or
  3. continuing to allow states to adopt their own planning strategies to show that PSD for NOx is satisfied through some combination of state and federal emissions controls that have been or will be adopted.

The proposal mentions scientific work sponsored by the National Park Service with respect to establishing "critical loads" related to nitrogen impacts on sensitive ecosystems. This scienctific information may be used as part of the basis for showing that PSD for NOx is satisfied under the third proposed option.

This proposed rule complies with a court order and the terms of a settlement agreement with Environmental Defense. The comment period closed on April 25, 2005. The final rule is expected in September 2005.

Congress is considering several bills that would build upon the success of the 1990 Clean Air Act program to reduce acid deposition by using a market-based national cap. President Bush supports the Clear Skies Act. The most recent draft of the Clear Skies Act would reduce national sulfur dioxide emissions from approximately 10 million tons per year to 4.5 million tons in 2010, then 3 millions tons in 2015 and beyond. National nitrogen oxide emissions would be reduced from approximately 4.5 million tons to 2.1 million tons in 2008 then to 1.7 million tons by 2015. This would be accomplished through two separate regional caps. The western cap would be approximately 0.5 million tons, the eastern cap would be approximately 1.2 million tons in 2015. Trading of nitrogen oxides emissions could take place within these two regions but not between them. The Clear Skies Act would also limit emissions of mercury to 26 tons in 2010 then to 15 tons in 2015. For the sources subject to these caps current programs for individual determination of control technologies and environmental impacts, including impacts on National Parks, would be waived or simplified.

In addition to the Clear Skies Act, Congress is considering two other "multi-pollutant" bills to reduce emissions from power plants. Senate Bill 150 (Jeffords) would reduce national sulfur dioxide emissions to 2.25 million tons by 2010 (0.27 million in the West, 1.97 million tons in the East). It would reduce nitrogen oxide emissions to 1.51 million tons by 2010 and mercury emissions to 5 tons in 2009 (no trading for Hg). In addition the Senate Bill 150 would cap carbon dioxide emissions at 2.05 billion tons in 2010. Senator Carper is working on legislation that would reduce sulfur dioxide emissions to 4.5 million tons in 2009, then 3.5 million in 2013, then 2.25 million tons in 2016 and beyond. The legislation would cap nitrogen oxide emissions at 1.87 million tons in 2009, dropping to 1.7 million in 2013. Mercury emissions would be capped at 24 tons in 2009 then 10 tons in 2013. Mercury reductions would be achieved by a percent reduction requirement at each source.

Anticipated Environmental Improvements
The Environmental Protection Agency has conducted an extensive assessment of the air quality benefits which are expected from implementation of the Clear Skies Act. Included in these analyses were expected improvements in visibility and acid deposition at "Class I" national park units. EPA projected a "Base Case" which includes future implementation of mobile source controls and nitrogen oxide reductions required to meet the one-hour ozone national ambient air quality standard. The Base Case projections do not include implementation of emissions reductions to meet the fine particle national ambient air quality standards (PM 2.5 ) or the first phase of the Regional Haze Rule requirements. The EPA used a combination of economic and air quality models to project future electrical generation and to solve for the least expensive way to meet the national and regional caps on emissions.

For more information on EPA's Clear Skies, please visit EPA's Clear Skies web page.

The links below display maps showing the expected changes in visibility and deposition.


Total Sulfur Deposition

Total Nitrogen Deposition

Get EPA's assessment of the human health and environmental benefits of Clear Skies in PDF format.

The following table provides the projections for specific Parks.

Park Visibility 2001-2020 Acid Deposition in 2020
Name Base**
Base +
Sulfur Deposition (kg/ha) Nitrate Deposition (kg/ha)
Base** Base+CSA Base** Base+CSA
Acadia -1 -2.0 3.6 3.0 2.5 2.3
Shenandoah -1.5 -3.5 7.9 6.0 5.8 5.1
Great Smoky Mountains -0.75 -2.5 8.4 7.4 6.2 5.2
Everglades -0.75 -1.0 3.5 3.2 2.2 2.0
Voyageurs -0.75 -1.25 2.5 2.2 4.1 3.5
Big Bend 0 -0.5 1.7 1.6 1.8 1.7
Rocky Mountain -0.5 -0.5 0.8 0.8 2.0 1.8
Yellowstone -0.75 -0.75 0.6 0.6 0.9 0.9
Glacier -0.75 -0.75 0.7 0.7 0.9 0.9
Sequoia -0.75 -0.75 0.7 0.7 1.5 1.5
Yosemite -1.5 -1.5 0.9 0.9 1.9 1.9
Mount Rainier -1.5 -1.5 1.2 1.2 0.9 0.8

*A deciview (dv) is a measure of visibility which captures the relationship between air pollution and human perception of visibility. When air is free of particles that cause visibility degradation, the deciview haze index is zero. The higher the level, the poorer the visibility. Decreases in the deciview index indicate improvements in visibility. A one deciview change translates to a just noticeable change in visibility for most individuals

**The Base Case projections do not include implementation of emissions reductions to meet the fine particle national ambient air quality standards (PM 2.5 ) or the first phase of the Regional Haze Rule requirements .

updated on 01/07/2007  I   http://www.nature.nps.gov/air/regs/newdev_clearSkies.cfm   I  Email: Webmaster