Regional haze affects visibility at national parks

The TCEQ is preparing to address federal concerns about regional haze at the Big Bend and Guadalupe Mountains national parks. Texas, as well as other states with national parks and wilderness areas, must submit plans this year for improved visibility. Texas will analyze the role that dust plays in regional haze, particularly at Guadalupe Mountains National Park.

In this story:
Geological Gems
Looking for Solutions
Plan Being Formulated
Sidebar: Dust Up in West Texas

At Big Bend National Park, hikers who make it to the highest parts of the Chisos Mountains often delight in the panoramic views. On a clear day, mountaintops in Mexico can be seen in the distance.

But the clear days are not so plentiful due to problems with visibility.

Big Bend and Guadalupe Mountains National Park, both in remote parts of West Texas, are destinations for a combined 500,000 vacationers each year.

However, the expectation of seeing grand vistas vanishes when visitors encounter a day marked by poor visibility. Big Bend has some of the densest regional haze of all the national parks in the western United States.

So what's affecting the views? Particulate matter. When sunlight encounters tiny pollution particles, which scatter and absorb the light, the result is haze.

State and federal studies show that haze-forming pollution comes from both natural and man-made sources. Windblown dust and soot from wildfires contribute to hazy skies, as do cars and trucks, electric power plants, manufacturing operations, and the practice of open burning. Particles from these activities can travel a long way from sources both inside and outside the United States before blowing across West Texas.

In the western states, which include Texas, hazy conditions in national parks reduce visibility from 140 miles under pristine conditions to a range of 35 to 90 miles, according to federal estimates.

Under the federal Regional Haze Rule, states are directed to work together in regional partnerships to improve visibility in 156 national parks and wilderness areas around the country. These protected areas include not only Big Bend and Guadalupe Mountains national parks, but also the Grand Canyon, Yosemite, Shenandoah, and the Great Smokies. Among Texas' neighbors, New Mexico has nine protected areas, Arkansas has two, and Oklahoma and Louisiana each have one.

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Geological Gems

Texas' two national parks are among the state's most valuable natural assets. The massive Big Bend National Park, which rivals Rhode Island in size, boasts of river, desert, and mountain environments. Visitors can ride the rapids down the Rio Grande one day and on the next day hike rugged mountains rising to 7,800 feet. The biological diversity and historical significance of the area provide rare opportunities for visitors to explore.

Guadalupe Mountains National Park features the highest point in the state: Guadalupe Peak at 8,749 feet. The park's ecological zones range from desert to high-altitude forest. The 2,000-foot-thick limestone layer of the Capitan Reef is regarded as one of the world's finest examples of ancient marine fossil reef, and is a draw for geologists from many countries.

Air quality at both parks is affected by a number of external factors. Big Bend's is influenced primarily by human activity, including smoke from agricultural burning in Mexico and Central America. The park at Guadalupe Mountains is more affected by dust storms that originate in desert areas in northern Mexico, southwestern New Mexico, and West Texas. (See "Dust Up in West Texas.")

The National Park Service operates monitoring equipment at both parks to track changes in air quality. These monitors collect visibility-reducing particles for laboratory analysis. It also has a webcam at Big Bend that displays the current visibility range.

The haziest days at Big Bend usually occur from April through October. High concentrations of smoke and dust begin to affect visibility in the spring, when farmers in southern Mexico and Central America burn crop remnants to clear their land, a practice that can lead to full-scale wildfires.

Among the man-made sources, sulfates represent the main contributor to impaired visibility. The source is sulfur dioxide (SO2), mainly from electric power plants, petroleum refineries, paper mills, and metal smelters in the midwestern and southern United States, in Texas, and in Mexico.

The transport of these particles for thousands of miles demonstrates the ability of pollutants to travel long distances.

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Looking for Solutions

The federal Regional Haze Rule does not require Texas to overcompensate, or over control, for emissions coming from outside the country. But for emission sources of U.S. origin, the Environmental Protection Agency has several regulatory programs concerned with regional haze.

Texas has adopted the federal Clean Air Interstate Rule (CAIR), which requires a net reduction by 2015 of more than 60 percent in SO2 and nitrogen oxides (NOx) from electric power plants among states in the program. The TCEQ has also adopted the Best Available Retrofit Technology (BART) program to ensure that large plants that were built before modern new source emission limitations were in place have no significant impact on visibility at protected national parks and wilderness areas.

The TCEQ adopted a BART rule in early 2007. Since then, modeling shows that 30 older industrial sources, all subject to review under the rule, have not had an impact on national parks and wilderness areas above EPA's specified threshold. Recently adopted legally enforceable reductions in emissions at several of these industrial sources resulted in the elimination of several thousand tons per year of haze-forming pollutants.

For emission sources within the state, the TCEQ points out that existing programs designed to reduce ozone also benefit visibility in national parks here and in surrounding states.

Texas has implemented comprehensive ozone control strategies in the areas of Houston-Galveston, Beaumont-Port Arthur, and Dallas-Fort Worth that are designed to reduce levels of NOx and volatile organic compounds, both of which contribute to ozone formation. Other urban areas have voluntary programs in place to lower ozone-forming emissions.

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Plan Being Formulated

To comply with the Regional Haze Rule, the TCEQ is revising the State Implementation Plan (SIP) to address visibility at both Big Bend and Guadalupe Mountains parks and at protected areas in neighboring states.

The federal rule calls for visibility improvements at national parks on the haziest days and no additional visibility impairment on the clearest days. It also requires states to take into account their impact on such areas in other states when determining their own reductions.

EPA has set a long-term goal to eliminate the effects of human activity on visibility by 2064, but for now states are concentrating on improvements for the next 10 years.

States are required to show that they are making reasonable progress toward meeting "natural visibility conditions"—the natural levels of particle concentrations that would exist without the influence of human activities. EPA is requiring the states to determine what the natural visibility conditions would be for their national park and wilderness areas.

Rather than using EPA's target for natural conditions at Big Bend and Guadalupe Mountains, the TCEQ has opted to develop refined estimates that take into account the recurrence of natural dust storms in the region.

To prepare for this summer's SIP submission to EPA, the TCEQ has held consultations with other states and with federal land managers from the National Park Service, U.S. Forest Service, and U.S. Fish and Wildlife Service.

Visit the SIP Revision: Regional Haze Web page for further information on the TCEQ's Regional Haze SIP.

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Dust Up in West Texas

Mention dust storms to anyone from West Texas, and there will be stories to follow. Tales about storms that brought highway traffic to a standstill or ripped cotton crops to shreds. Swirling dust and sand, propelled by high gusts, can be so dense that the midday sun all but disappears.

While these high-wind events vary in intensity, all dust storms affect visibility to some degree.

Dust storms contribute to some of the major regional haze and particulate matter episodes measured in West Texas, according to TCEQ studies. Dust is certainly a factor in calculating visibility at the two federally run parks in West Texas, especially at Guadalupe Mountains National Park.

Both rugged parks at the Guadalupe Mountains and Big Bend are located in the Chihuahuan Desert, which is characterized by limited rainfall, sparse vegetation, and high winds. Stretching from northern Mexico into Texas, New Mexico, and Arizona, the Chihuahuan Desert is one of four major dust storm areas in the United States.

The number of dust storms in West Texas ranges from five to 25 a year. The frequency and the intensity of these weather events depend on factors such as weather and the moisture content of the soil.

Data gathered from air quality monitors and meteorological equipment show that the park at Guadalupe Mountains had 48 dust storms from 2000 to 2004, while Big Bend had 23 in the same period.

During the worst visibility days at the Guadalupe Mountains, dust is responsible for about 50 percent of the visual impairment; at Big Bend, it is 20 percent.

Dust storms are recurring, natural events and therefore cannot be controlled. The TCEQ maintains that the inevitability of dust storms should be given considerable weight in developing plans for improved visibility at the state's two national parks over the coming decades.

A Day for the Record Books

For Texas, the worst dust storm recorded in recent years occurred April 15, 2003. The El Paso airport reported visibility as low as one-eighth of a mile with peak wind gusts of 66 miles per hour. The high winds were associated with a strong low pressure system centered in Colorado, which kicked up large plumes of dust in New Mexico and West Texas.

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