For more information about National Park Service air resources, please visit http://www.nature.nps.gov/air/.
Air Pollution Impacts
Big Bend National Park
Natural and scenic resources in Big Bend National Park (NP) are susceptible to the harmful effects of air pollution. Fine particles, nitrogen, ozone, and toxics impact scenic resources such as visibility, and natural resources such as surface waters, fish, and vegetation. Click on the tabs below to learn more about air pollutants and their impacts on natural and scenic resources at Big Bend NP.
- Nitrogen & Sulfur
- Toxics & Mercury
Many visitors come to Big Bend NP to enjoy panoramic vistas of the ribbon-like Rio Grande, or endless miles of Chihuahuan Desert. Unfortunately, these vistas are often obscured by haze caused by fine particles in the air; oftentimes the result of nearby coal-burning power plants. Many of the same pollutants that ultimately fall out as nitrogen and sulfur deposition contribute to this haze and visibility impairment. Organic compounds, soot, and dust reduce visibility as well.
Visibility effects at Big Bend NP include:
- Reduction of the average natural visual range from about 160 miles (without the effects of pollution) to about 70 miles because of pollution at the park;
- Reduction of the visual range from about 120 miles to below 40 miles on high pollution days;
- Frequent impairment of scenic vistas by haze.
(Source: IMPROVE 2010)
- Explore scenic vistas through a live webcam at Big Bend National Park!
- Learn about the Big Bend Regional Aerosol and Visibility Observations (BRAVO) Study, an investigation into the causes of visibility reducing hazes at the park (NPS 2004; BRAVO Fact sheet [pdf, 157 KB]).
- Sulfate particles are the single largest contributor to haze at the park. Sources of this secondary pollutant include coal-fired power plants, metal smelters, refineries, other industrial processes, and volcanoes (Pitchford et al. 2004).
- Episodes of high pollution at the park are the result of emission from sources in East Texas, the Gulf Coast (Houston and Galveston) and U.S. states further to the north and east, as well as northeastern Mexico (Monterrey and Monclova) and Mexico City (Pitchford et al. 2004).
Nitrogen (N) and sulfur (S) compounds deposited from air pollution can harm surface waters, soils, and vegetation. N and S deposition cause acidification of streams and lakes in some parts of the country, while N deposition is known to disrupt soil nutrient cycling and alter aquatic and plant communities. Surface waters at Big Bend NP are likely to be well-buffered from acidification because of an abundance of base cations like calcium in the soils and rocks. However, arid, upland areas in the park are sensitive to fertilization from excess nitrogen. The sparse native vegetation in the park is not adapted to higher nitrogen levels and therefore may be displaced by invasive species like cheatgrass. Such non-native species can readily take up nitrogen and use it to their advantage.
Potential effects of nitrogen and sulfur deposition at Big Bend NP include:
- A decrease in soil microbe diversity as nitrogen increases, evidenced by fertilization experiments in the high elevation oak and pine forest;
- Increased fire risk in the park, as the interaction of climate change and increased nitrogen enhances vegetation coverage and provides fuel;
- Higher concentrations of nitrates in grasslands soil samples and changing soil pH.
(Source: Zak 2006)
Naturally-occurring ozone in the upper atmosphere absorbs the sun’s harmful ultraviolet rays and helps to protect all life on earth. However, in the lower atmosphere, ozone is an air pollutant, forming when nitrogen oxides from vehicles, power plants, and other sources combine with volatile organic compounds from gasoline, solvents, and vegetation in the presence of sunlight. In addition to causing respiratory problems in people, ozone can injure plants. Ozone enters leaves through pores (stomata), where it can kill plant tissues, causing visible injury, or reduce photosynthesis, growth, and reproduction.
Big Bend NP has several ozone-sensitive plants including Rhus trilobata (skunkbush) and Pinus ponderosa (ponderosa pine). Ozone concentrations and cumulative doses are at levels in the park known to cause injury to such sensitive plants. However, the generally dry conditions in the park cause increased plant pore (stomatal) closures, thereby reducing ozone uptake by plants and the injury that results.
Search the list of ozone-sensitive plant species (pdf, 184 KB) found at each national park.
Toxics, including heavy metals like mercury, accumulate in the tissue of organisms and may alter key ecosystem processes. When mercury converts to methylmercury in the environment and enters the food chain, effects can include reduced reproductive success, impaired growth and development, behavioral abnormalities, reduced immune response, and decreased survival. Human activities have greatly increased the amount of mercury in the environment through processes such as burning coal for electricity and burning waste. Other toxic air contaminants of concern include pesticides, industrial by-products, and emerging chemicals such as flame retardants for fabrics. Some of these toxics are also known or suspected to cause cancer or other serious chronic health effects in humans and wildlife. Such environmental toxins present a concern for natural resources as well as park visitors and locals who fish for pleasure or sustenance.
Effects of airborne toxics on ecosystems at Big Bend NP include:
- Elevated concentrations of current-use pesticides (chlorpyrifos, endosulfans, dacthal, and lindane) found in park vegetation samples; concentrations of current-use pesticides ranked at or above the median as compared to other national park sites studied (Landers et al. 2010; Landers et al. 2008);
- Presence of dioxins, PCBs, and related compounds in park air samples, which could adversely affect wildlife in the park (Cleverly et al. 2000 [pdf, 110 KB]);
- High levels of DDE (a breakdown product of DDT) and mercury found in birds of prey, such as peregrine falcons, which may correspond to impaired peregrine falcon reproduction (Mora et al. 2002).
Studies and monitoring help the NPS understand the environmental impacts of air pollution. Access air quality data and see what is happening with Studies and Monitoring at Big Bend NP.
Last Updated: June 14, 2011