Big Bend National Park

Elephant TuskAir Quality & Visibility
in Big Bend National Park

How Far Can You See?
Big Bend National Park--the name inspires varied impressions of the Southwest. One portrait is of majestic mountains towering above rugged badlands. Another is of the ribbon-like Rio Grande charging through sheer-walled canyons. But most commonly, Big Bend evokes images of panoramic vistas panning across endless miles of Chihuahuan Desert as far as the eye can see. As far as the eye can see--perhaps? On some days of the year Big Bend’s air quality is so good that visitors can actually see the detail of large objects over 100 miles away. Unfortunately, pollution is destroying the very scenic resources many people seek. Generally, park visitors find moderately hazy views on most days, with poor conditions of less than 30 miles visibility 6% of the time. On a few days of the year Big Bend experiences the worst air quality, in terms of visibility impairment, within any western national park!

Good Air   Bad Air
These photos show the same view on a day with
good visibility and a day with poor visibility.

Parks and the Clean Air Act
The goal of the 1970 Clean Air Act is safe and acceptable ambient air quality. The Act directs that “Primary” air standards be set to protect public health. “Secondary” standards protect the national welfare including resources and values found in the national parks.

The Act seeks to “prevent the significant deterioration” of air quality, particularly in areas of special natural, scenic, or historic values. These regions are classified as “class I areas” and include many western national parks, one of which is Big Bend.

By enacting clean air legislation, Congress expressed the national desire to preserve the scenic values we have come to expect in our national parks.

Current Knowledge
In spite of Big Bend’s remote location and presumed immunity to such urban problems as air pollution, noticeable changes in the park’s air quality appeared during the 1970s. In response to this impending threat, park managers began an air monitoring program in 1978. After years of data collection and analysis, researchers are now able to interpret the transport and transformation of pollutants that contribute to the park’s reduced visibility.

Following are some of the major sources that contribute to Big Bend’s visibility pollution:

   • North Central Mexico including the urban and industrial region of Monterrey and Monclova.
   • East-Central Texas and the Gulf Coast, including the urban and industrial areas of Houston and Galveston.
   • Mexico City and its surrounding urban area.
   • Windblown soil and dust.

TransmissometerMonitoring Program
Big Bend’s monitoring program includes many data collection systems:

4. Automated Camera System - a permanently mounted camera that takes photos of the same distant scene at 9:00 am, 12 noon, and 3:00 pm each day, providing a daily account of visibility. One camera posts a picture to the Park's website every 15 minutes. 

5. Precipitation Chemistry Analysis - part of a nationwide system which monitors changes in the chemistry and acid content of precipitation. Big Bend has participated in this program since 1980.

6. Ozone Monitor - a device that measures ozone in the atmosphere on a continuous basis.

7. Polyurethane Foam Sampler - Samples air and measures amounts of lead, PCB's, and volatile organics.

The Wind Blows Where It Will
Air quality in this area varies significantly by season, with the summer season typically having the poorest visibility and winter season the best. Summer winds are from the southeast while winter winds are from the north and west. Nearly half of Big Bend’s visibility reduction is due to sulfates. During the summer, air masses arriving in this region from the southeast bring the highest concentrations of sulfates and the poorest visibility conditions.

Where is Today's Air Coming From?
view the trajectory maps

Using back-trajectory analysis, researchers can back-track prevailing wind patterns and trace the origin of pollutants. A typical summer wind pattern for Big Bend may begin two days earlier in East Texas, circulate into Louisiana, dip south along the Gulf Coast, migrate west into Mexico, and finally blow toward the northwest into this area. This wind pattern may collect, transport, and deliver such pollutants as sulfates, organic carbons, nitrates, and wind blown soil particles.

Nearly half of Big Bend's visibility reduction is due to sulfates. Data suggest that sulfur emissions from nearby Texas and Mexican coal-fired power plants and industrial processes help create the white haze that often diminishes or obscures the scenic landscapes in Big Bend National Park.

The B.R.A.V.O. Study
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.

When the results are released, park managers hope to gain a deeper understanding of what is causing the decline in park visibility and a wealth of needed information on how to protect the wonderful views of Big Bend National Park.

What You Can Do
Let people know that you care. Learn about local efforts and issues. Public libraries contain references on various topics addressing air pollution. Talk to your state or federal environmental agency to find out what it is doing in your area.

For more information on air quality in Big Bend National Park write to:

During your visit to Big Bend join a ranger for a guided walk or evening presentation to learn more about issues affecting park resources.

Get involved in local efforts by supporting ballot measures and candidates sensitive to air quality issues.

Since automobiles are a major source of air pollution, how you drive and care for your car is important. Use an energy-conserving grade motor oil, use reformulated or “clean” fuels, and drive at a medium speed. Most cars operate most efficiently between 35 and 55 miles per hour. Keep your engine tuned and maintain the correct tire pressure.

Electricity generation can be a source of air pollution. At home and at work save electricity by using energy-efficient lighting wherever possible. Ask your utility company about its customer energy conservation program. Purchase energy-efficient appliances.

Air Quality in National Parks
Webcams, research, monitoring, etc.