In 1999, the Environmental Protection Agency issued a new regulation called the Regional Haze Rule. It calls for state and federal agencies to work together to improve visibility in 157 National Parks and wilderness areas, including Big Bend National Park. Analyses must be conducted to ensure that they reach natural background conditions within the next sixty years.

That same year, the Environmental Protection Agency and the National Park Service teamed up to carry out the most sophisticated air pollution study every conducted, the B.R.A.V.O.

Objectives of this study were to quantify the impacts of major pollution sources from Mexico and the United States on Big Bend National Park, determining what makes up park air pollution, the role of weather in park haze, and the paths that air pollution follows to reach the park. Data was collected from 42 different sites throughout Texas. Chemical tracers were released from specific locations and their movements were "tracked" by sensitive air samplers.

The final report, released in September of 2004, contains a number of surprising results regarding the sources of air pollution in the Big Bend region.

BRAVO Results Fact sheet [157k PDF File]
BRAVO Final Report (September 2004)