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Big Bend Air Study Released

Release Date: 9/17/2004
Contact Information: For more information contact the Office of External Affairs at (214) 665-2200.

      Sulfates resulting from sulfur dioxide (SO2) make up more than half (55 percent) of the haze that impairs visibility in Big Bend National Park.  The conclusion is part of the Big Bend Regional Aerosol and Visibility Observational (BRAVO) study report released today by the U.S. Environmental Protection Agency (EPA), the National Park Service (NPS) and the Texas Commission on Environmental Quality (TCEQ).

      The study found that on the worst days, visibility-reducing sulfates from states to the east and north of Texas were responsible for approximately 22 percent of the man-made haze at the park.  SO2 from Mexico, primarily from the two Carbón power plants, accounted for approximately 16 percent, while 11 percent of the man-made haze was caused by SO2 emissions in Texas.

      The BRAVO study to assess the causes of haze at Big Bend involved intensive monitoring from July through October 1999 followed by a four-year data analysis and modeling effort.   It is considered one of the largest and most complicated fine-particulate/haze field studies ever attempted. It includes state-of-the-science techniques, including release, sampling, and analysis of inert atmospheric tracers from potentially major contributing sources over a distance of more than 500 miles.

      Since the timeframe utilized in this study, several actions have occurred in the United States that have reduced haze-forming emissions, or will contribute to such reductions in the future.  In 2004, for example, the NOX SIP call involving 19 eastern states and the District of Columbia came fully into effect, limiting the amount of nitrous oxides emitted by power plants in the affected states.  Phase II of the acid rain program, which limits emissions of sulfur dioxide from power plants, was also implemented in 2000.

      In coming years, the Clean Air Interstate Rule (CAIR) will provide additional, dramatic reductions in sulfur dioxide and nitrogen dioxide emissions in many eastern states.  This program, due to be finalized by the end of 2004, would utilize a cap-and-trade program to provide cost-effective reductions in pollution and will ultimately result in a 70 percent reduction in emissions of sulfur dioxide and a 65 percent reduction in emissions of nitrous oxides from current levels.  This is the same type of program utilized by the successful acid rain program which has helped to reduced sulfur dioxide emissions by approximately 7 million tons per year since 1990.

      The BRAVO study report is available at