- Air quality at Big Bend National Park
- Related references
Air quality at Big Bend National Park
Most visitors expect clean air and clear views in parks. Big Bend National Park (NP), Texas, home to mountain, desert, and river environments, lies downwind of major pollution sources in eastern Texas, other U.S. states, and Mexico. The National Park Service works to address air pollution effects at Big Bend NP, and in parks across the U.S., through science, policy and planning, and by doing our part.
Many visitors come to Big Bend NP to enjoy panoramic vistas of the ribbon-like Rio Grande, or seemingly endless miles of Chihuahuan Desert. Unfortunately, park vistas are often obscured by haze, reducing how well and how far people can see. Visibility reducing haze is caused by tiny particles in the air, and these particles can also affect human health. Many of the same pollutants that ultimately fall out as nitrogen and sulfur deposition contribute to this haze. Organic compounds, soot, and dust reduce visibility as well.
The NPS and the Environmental Protection Agency (EPA) conducted the Big Bend Regional Aerosol and Visibility Observational (BRAVO) study to explore haze in the park (NPS 2004; BRAVO). The BRAVO study found that sulfate particles are the single largest contributor to haze in the park. Sulfate emission sources include coal-fired power plants, metal smelters, refineries, other industrial sources, and volcanoes. Emission sources from eastern Texas and eastern states in the U.S. on average contribute 55% to the haziest days at Big Bend NP (Pitchford et al. 2004). Federal regulations that reduce sulfur dioxide emissions should make progress toward improving visibility at the park. Sources in Mexico were also shown to contribute to visibility impairment at Big Bend NP, and partnerships between agencies in Mexico and the U.S., such as Border 2020, have been established to address the transport of pollution.
Significant improvements in park visibility on clearest days have been documented since the late 1980’s. There is no significant trend on haziest days over the same time period and visibility in the park remains a long way from the Clean Air Act goal of no human caused impairment.
- Reduction of the average natural visual range from about 165 miles (without the effects of pollution) to about 90 miles because of pollution at the park
- Reduction of the visual range from about 120 miles to below 55 miles on high pollution days
Visit the NPS air quality conditions and trends website for park-specific visibility information. Big Bend NP has been monitoring visibility since 1988. Check out the live air quality webcam and explore air monitoring »
Nitrogen and sulfur
Nitrogen and sulfur compounds deposited from the air may have harmful effects, including acidification, on soils, lakes, ponds, and streams. 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. Some plant species are sensitive to acidification, search for acid-sensitive plant species found at Big Bend NP.
Excess nitrogen can also lead to nutrient enrichment, a process that changes nutrient cycling and alters plant communities. Healthy ecosystems can naturally buffer a certain amount of pollution, but as nitrogen and sulfur accumulate, a threshold is passed where the ecosystem is harmed. “Critical load” is a term used to describe the amount of pollution above which harmful changes in sensitive ecosystems occur (Porter 2005). Arid, upland areas in the park are sensitive to fertilization from excess nitrogen. Ecosystems at Big Bend NP are considered very highly sensitive to nitrogen-enrichment effects relative to all Inventory & Monitoring parks (Sullivan et al. 2011c; Sullivan et al. 2011d). The sparse native vegetation in the park is not adapted to higher nitrogen levels and may be displaced by invasive species like cheatgrass. Such non-native species can readily take up nitrogen and spread quickly.
Effects of nitrogen and sulfur:
- A decrease in soil microbe diversity as nitrogen increases, evidenced by fertilization experiments in the high elevation oak and pine forest (Zak 2006);
- Increased fire risk in the park, as the interaction of climate change and increased nitrogen enhances vegetation coverage and provides fuel (Zak 2006);
- Higher concentrations of nitrates in grasslands soil samples and changing soil pH (Zak 2006).
- Nitrogen deposition exceeds the critical load for one or more park ecosystems (NPS ARD 2018).
Visit the NPS air quality conditions and trends website for park-specific nitrogen and sulfur deposition information. Big Bend NP has been monitoring atmospheric deposition of nitrogen and sulfur since 1980. Explore air monitoring »
At ground level, ozone is harmful to human health and the environment. Ground-level ozone does not come directly from smokestacks or vehicles, but instead is formed when other pollutants, mainly nitrogen oxides and volatile organic compounds, react in the presence of sunlight.
Over the course of a growing season, ozone can damage plant tissues making it harder for plants to produce and store food. It also weakens plants making them less resistant to disease and insect infestations. Big Bend NP has several ozone-sensitive plants including Rhus aromatica (fragrant sumac) and Salix exigua (desert willow). Ozone concentrations and cumulative doses are high enough in the park to cause injury to sensitive plants. However, dry conditions in the park cause increased plant pore (stomatal) closures, which reduces ozone uptake and injury. Search ozone-sensitive plant species found at Big Bend NP.
Visit the NPS air quality conditions and trends website for park-specific ozone information. Big Been NP has been monitoring ozone since 1990. Check out the live ozone and meteorology data from Big Bend NP and explore air monitoring »
Mercury and toxics
Airborne mercury, and other toxic air contaminants, when deposited are known to harm birds, salamanders, fish and other wildlife, and cause human health concerns. These substances enter the food chain and accumulate in the tissue of organisms causing reduced reproductive success, impaired growth and development, and decreased survival.
Mercury and toxics effects:
- Elevated concentrations of current-use pesticides (chlorpyrifos, endosulfans, dacthal, and lindane) found in park vegetation samples (Landers et al. 2010; Landers et al. 2008);
- Concentrations of pesticides ranked at or above the median among 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 harm wildlife in the park (Cleverly et al. 2000);
- 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).
Cleverly, D. H., D. Winters, J. Ferrario, J. Schaum, G. Schweer, J. Buchert, C. Greene, A. Dupuy, C. Byrne. The National Dioxin Air Monitoring Network (NDAMN): Results of the First Year of Atmospheric Measurements of CDDs, CDFs, and Dioxin-Like PCBs in Rural and Agricultural Areas of the United States: June 1998–June 1999. Presented at Dioxin ’00, 20th International Symposium on Halogenated Environmental Organic Pollutants & POPS, held Aug 13–17 at Monterey, CA. Short paper in, Organohalogen Compounds 45: 248–251.
Kohut R.J. 2007. Ozone Risk Assessment for Vital Signs Monitoring Networks, Appalachian National Scenic Trail, and Natchez Trace National Scenic Trail. NPS/NRPC/ARD/NRTR—2007/001. National Park Service. Fort Collins, Colorado. Available at https://www.nps.gov/articles/ozone-risk-assessment.htm
Landers, D. H., Simonich, S. M., Jaffe, D., Geiser, L., Campbell, D. H., Schwindt, A., Schreck, C., Kent, M., Hafner, W., Taylor, H. E., Hageman, K., Usenko, S., Ackerman, L., Schrlau, J., Rose, N., Blett, T., Erway, M. M. 2010. The Western Airborne Contaminant Assessment Project (WACAP): An Interdisciplinary Evaluation of the Impacts of Airborne Contaminants in Western U.S. National Parks. Environmental Science and Technology 44: 855–859.
Landers, D. H., S. L. Simonich, D. A. Jaffe, L. H. Geiser, D. H. Campbell, A. R. Schwindt, C. B. Schreck, M. L. Kent, W. D. Hafner, H. E. Taylor, K. J. Hageman, S. Usenko, L. K. Ackerman, J. E. Schrlau, N. L. Rose, T. F. Blett, and M. M. Erway. 2008. The Fate, Transport, and Ecological Impacts of Airborne Contaminants in Western National Parks (USA). EPA/600/R—07/138. U.S. Environmental Protection Agency, Office of Research and Development, NHEERL, Western Ecology Division, Corvallis, Oregon. Available at https://irma.nps.gov/DataStore/Reference/Profile/660829.
Mora, M., Skiles, R., McKinney, B., Paredes, M., Buckler, D., Papoulias, D., Klein, D. 2002. Environmental contaminants in prey and tissues of the peregrine falcon in the Big Bend Region, Texas, USA. Environ Pollut. 116 (1): 169–176.
[NPS] National Park Service. 2004. Understanding Haze in Big Bend National Park—Big Bend Regional Aerosol and Visibility Observational (BRAVO) Study. Fact sheet. Available at http://vista.cira.colostate.edu/Improve/big-bend-regional-aerosol-and-visibility-observational-bravo/
Pitchford, M. L., Tombach, I., Barna, M., Gebhart, K. A., Green, M. C., Knipping, E., Kumar, N., Malm, W. C., Pun, B., Schichtel, B. A., Seigneur, C. 2004. Big Bend Regional Aerosol and Visibility Observational Study Final Report. Available at http://vista.cira.colostate.edu/Improve/final-report-bravo/
Sullivan, T. J., McDonnell, T. C., McPherson, G. T., Mackey, S. D., Moore, D. 2011a. Evaluation of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from atmospheric nitrogen deposition: main report. Natural Resource Report NPS/NRPC/ARD/NRR—2011/313. National Park Service, Denver, Colorado. Available at https://www.nps.gov/articles/nitrogen-risk-assessment.htm
Sullivan, T. J., McDonnell, T. C., McPherson, G. T., Mackey, S. D., Moore, D. 2011b. Evaluation of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from atmospheric nitrogen deposition: Chihuahuan Desert Network (CHDN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/330. National Park Service, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2168613
Sullivan, T. J., McPherson, G. T., McDonnell, T. C., Mackey, S. D., Moore, D. 2011c. Evaluation of the sensitivity of inventory and monitoring national parks to acidification effects from atmospheric sulfur and nitrogen deposition: main report. Natural Resource Report NPS/NRPC/ARD/NRR—2011/349. National Park Service, Denver, Colorado. Available at https://www.nps.gov/articles/acidification-risk-assessment.htm
Sullivan T.J. 2016. Air quality related values (AQRVs) in national parks: Effects from ozone; visibility reducing particles; and atmospheric deposition of acids, nutrients and toxics. Natural Resource Report. NPS/NRSS/ARD/NRR—2016/1196. National Park Service. Fort Collins, Colorado. Available at https://www.nps.gov/articles/aqrv-assessment.htm
Zak, J. 2006. Impacts of Atmospheric Nitrogen Deposition and Climate Change on Desert Ecosystems. Big Bend National Park. NPS Final Report. 15 pp.