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SO2 Emission Reductions from Acid Rain Program Sources and Improvements in Air Quality

Cap and Trade

Since its inception in 1990, the cap and trade component of the Acid Rain Program (ARP) has reduced SO2 emissions from power plants by 10 million tons (more than 60 percent). The program is currently at full implementation, with a permanent cap on SO2 emissions at 8.95 million tons, or about a 50 percent reduction from 1980 levels.

To date, EPA's cap and trade programs have delivered significant environmental results. The interactive map below demonstrates the success of these programs.

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(Clicking on the Play button in the bottom left corner of the map sets the map in motion.)

The green dots on the map above show emissions of SO2 from ARP sources—3,500+ power generating units greater than 25 MW (the largest being primarily coal burning). Note that at the program’s inception in 1995, SO2 emissions drop significantly and decrease further over time. The colored background is an isopleth map showing change in sulfate concentrations as measured by the CASTNET rural air quality monitoring network, leading to significant improvements in air quality and human health.

Wet sulfate deposition decreased 43 percent in the Northeast and 44 percent in the Midwest under the ARP. Wet nitrogen deposition also decreased in the Northeast by 27 percent and in the Midwest by 16 percent. These reductions in sulfur and nitrogen deposition have resulted in positive changes in environmental indicators, including improved water quality in lakes and streams.

The program has reduced SO2 emissions faster and at far lower costs than anticipated, yielding wide-ranging health and environmental improvements. A 2003 Office of Management and Budget study (PDF) (234 pp, 2.4M, About PDF) found that the ARP accounted for the largest quantified human health benefits—over $70 billion annually—of any federal regulatory program implemented in the last 10 years, with annual benefits exceeding costs by more than 40:1―for every dollar spent on implementing this cap and trade program, 40 dollars are returned in health and environmental benefits. A 2005 study (PDF) (15 pp, 532K, About PDF) estimated the program’s benefits at $122 billion annually in 2010, while cost estimates are around $3 billion annually (in 2000 dollars).

The program covers more than 3,500 sources and has had near perfect compliance. Sources found to have exceeded their emission allowances were assessed automatic penalties. Stringent emissions monitoring and transparent data ensure program integrity, and a robust allowance trading market has emerged.

* Note that there are no data for SO2 emissions prior to 1990. Power plant emissions between 1990 and 1994 were based on estimates; in 1995, continuous emissions monitoring systems (CEMS) were required of all program sources.

These animations are based on data and interactive mapping applications at EPA's Airmarkets website. For complete ARP and NBP data overlay files, as well as air quality and deposition data for interactive mapping applications (i.e., Google Earth), go to the Airmarkets Interactive Mapping page.

Additional Resources

Air Quality and Deposition Data and Maps

Emissions Monitoring Data


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