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Clear Skies

EPA'S 2003 Modeling of Clear Skies: Why EPA Revised its Modeling

Information provided for informational purposes onlyNote: EPA no longer updates this information, but it may be useful as a reference or resource.
Unless otherwise noted, the data presented throughout this Web site reflect EPA’s 2003 modeling and analysis of the Clear Skies Act of 2003. Clear Skies legislation was intended to create a mandatory program that would dramatically reduce power plant emissions of sulfur dioxide (SO2), nitrogen oxides (NOx), and mercury by setting a national cap on each pollutant. The Clear Skies bill was proposed in response to a growing need for an emission reduction plan that will protect human health and the environment while providing regulatory certainty to the industry. The proposed legislation for air regulation never moved out of the Senate Environment and Public Works committee in 2005 and was therefore never enacted.

July 1, 2003

Last year, EPA completed sophisticated modeling of emissions, air quality, deposition, and water quality to project the effect of the Clear Skies Act of 2002.

EPA has now updated the modeling analyses to incorporate new factual information, new state and federal regulations, advances in modeling, and other changes that were not incorporated in the modeling last year, per descriptions below:

Legislative Changes

  • To be consistent with the changes in the Clear Skies legislation between 2002 and 2003, Oklahoma and Kansas are included in the western zone for NOx requirements. They were moved to the western zone because we believe they do not significantly contribute to PM2.5 or ozone nonattainment problems.

New Air Pollution Control Programs

  • Several states have adopted power plant requirements that were not incorporated into last year's analyses and are now added. (e.g., North Carolina's Clean Smokestacks Act and other state laws adopted before April 2003).
  • EPA's proposed a nonroad diesel engine rule, which will help reduce ozone and fine particle pollution has been added to the new analyses.

New Air Quality and Emissions Data

  • EPA has more recent air quality monitoring data (1999-2001) to determine current attainment with the ozone and PM2.5 standards. This data shows that the air is cleaner and that more counties currently meet the standards compared to the previous Clear Skies analyses.
  • A 2001 inventory of emissions from all sectors was used instead of a 1996 inventory.

Updated Power Sector Assumptions

  • EPA used updated assumptions related to the power sector, including: more current information on costs and performance of mercury controls; higher electricity demand growth rate; higher natural gas prices; updated information about existing generation capacity; updated inventory of NOx and SO2 controls; updated cost and performance of new conventional units and existing nuclear units; updated renewable energy programs and portfolio standards; fuel oil assumptions; coal supply curves; and Acid Rain Program emissions allowance bank.

Sensitivity Analyses

  • EPA's new analyses include several sensitivity analyses to project the effects of using alternative assumptions by the Energy Information Agency about natural gas prices, electricity growth, and mercury emissions.

Updated Air Quality and Attainment Modeling

  • To project future PM2.5 attainment more accurately, EPA used a refined technique which relies on data from air quality monitors that "speciate" particles (e.g., identify particles as nitrates, sulfates, organics).
  • An updated version of the REMSAD model was also used to project air quality and deposition. REMSAD (the Regional Model System for Aerosols and Deposition) is a three-dimensional grid model designed to calculate concentrations of air pollution by simulating physical and chemical processes in the atmosphere.

New or Updated Health Benefits Data and Modeling Methods

  • The health benefits model was updated with new census data (2000 data instead of 1990).
  • New health effects endpoints (non-fatal heart attacks and school loss days) were added to the modeling.
  • Updated concentration-response functions were used for hospital admissions and ER visits for asthma.
  • The alternative estimate calculations for valuing premature mortality were updated.

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