Series: Park Air Profiles

Park Air Profiles - Grand Canyon National Park

Desert Viewpoint, Grand Canyon National Park
Visitors come to Grand Canyon National Park to enjoy scenic views of unique geology at one of the largest canyons in the world.

Air quality at Grand Canyon National Park

Most visitors expect clean air and clear views in parks. Grand Canyon National Park (NP), Arizona, world-renowned for its breathtakingly iconic views, is downwind of air pollution from coal-fired power plants in the Four Corners region, nearby mining, and urban and industrial pollutants from Mexico and California. Air pollutants carried into the park can harm natural and scenic resources such as forests, soils, streams, fish, and visibility. The National Park Service works to address air pollution effects at Grand Canyon NP, and in parks across the U.S., through science, policy and planning, and by doing our part.

Visibility

Grand Canyon, NP Clean, clear air is essential to appreciating the scenic vistas at Grand Canyon NP.

At Grand Canyon NP, scenic views are often affected by haze that reduces 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. Most of the fine particles affecting the Grand Canyon NP travel long distances from urban and industrial areas, mixing en route to form a uniform “regional haze” that obscures scenic vistas.

Visibility effects:
  • Reduction of the average natural visual range from about 175 miles (without the effects of pollution) to about 140 miles because of pollution
  • Reduction of the visual range from about 120 miles to below 90 miles on high pollution days

There has been extensive visibility research at Grand Canyon NP, especially from the late 1970s to the late 1990s. Projects like the Winter Haze Intensive Tracer Experiment (WHITEX) and Measurement of Haze and Visual Effects (Project MOHAVE) focused on determining sources of visibility impairment at the park (Malm et al., 1989; Pitchford et al., 1999). Such research identified coal-fired power plants, copper smelters, urban areas like southern California and Las Vegas, and wildland fire as the most significant sources of haze for the park. As reductions in human-caused air pollution have been achieved, the significance of smoke on visibility impairment has increased.

Additionally, research at Grand Canyon NP has improved the general understanding of visibility processes. Investigations centered on the primary visibility impairing compounds and the role of water vapor in reducing visibility (Wilson and McMurry, 1982; Pitchford and McMurry, 1994; Malm and Day, 2001).

The State of Arizona and Western Regional Air Partnership (WRAP) work together to address regional sources of haze affecting Grand Canyon NP. WRAP is a voluntary organization of Western states, tribes, and federal agencies that works to develop new technical and policy tools that help Western states meet Environmental Protection Agency haze regulations. Other federal agencies involved include the Bureau of Land Management, Fish & Wildlife Service, and U.S. Forest Service.

Visit the NPS air quality conditions and trends website for park-specific visibility information. Grand Canyon NP has been monitoring visibility since 2000. 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. About half of the nitrogen and a third of the sulfate deposited in Grand Canyon NP ecosystems comes down in rain and snow as “wet deposition.” The rest is “dry deposition” of particles, dust, and droplets. Surface water chemistry data for Grand Canyon NP indicate that park surface waters are well buffered and not likely to be acidified by atmospheric deposition. Soils are also well-buffered from acidification (Binkley et al. 1997). Still, some plant species may be sensitive to acidification, search for acid-sensitive plant species found at Grand Canyon NP.

Excess nitrogen can also lead to nutrient enrichment, a process that changes nutrient cycling and alters plant communities. Vegetation communities in the park have evolved under low nitrogen conditions and are likely to be very sensitive to nutrient enrichment. Excess nitrogen may allow more weedy, invasive plants to out-compete native species, reducing biodiversity (Fenn et al. 2003). 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). 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. Grand Canyon NP has been monitoring atmospheric deposition of nitrogen and sulfur since 1981. Explore air monitoring »

Ground-level ozone

Ponderosa Pine trees are one of the ozone sensitive species found at Grand Canyon NP. Ponderosa Pine trees are one of the ozone sensitive species found at Grand Canyon NP.

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.

During the summer months, ozone levels in the park sometimes exceed the National Ambient Air Quality Standards set by the U.S. Environmental Protection Agency to protect public health. Ozone is a respiratory irritant, causing coughing, sinus inflammation, chest pains, scratchy throat, lung damage, and reduced immune system functions. Children, the elderly, people with existing health problems, and active adults are most vulnerable.

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. Ozone concentrations sometimes reach levels known to be harmful to plants at Grand Canyon NP. Pinus ponderosa (ponderosa pine) is known to be sensitive to ozone. However field surveys of Ponderosa pine in 1992–93 and 2008 did not document any ozone injury (Binkley et al. 1997; NPCA 2010). Dry conditions typical of the park cause plants to close their stomata to conserve water. This limits ozone uptake and injury. Plants in riparian areas however, are adequately watered and may uptake enough ozone to cause injury. Also, unlike urban areas, where ozone concentrations typically fall at night, summer ozone levels often remain elevated at Grand Canyon NP. Higher nighttime ozone levels may increase damage potential for drought-adapted plant species that respire at night. Some plants are more sensitive to ozone than others, search ozone-sensitive plant species found at Grand Canyon NP.

Visit the NPS air quality conditions and trends website for park-specific ozone information. Grand Canyon NP has monitored ozone concentrations on the South Rim continuously since 1989. Check out the live ozone and meteorology data from Grand Canyon 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.

Concentrations of mercury and other metals in the Colorado River have exceeded EPA drinking water criteria at times (NPS 1996). Because the Colorado River in Grand Canyon NP receives inputs from many watersheds upstream, it is likely that contaminants come from a combination of atmospheric deposition, runoff, and mine drainage. Such environmental toxins present a concern for natural resources as well as park visitors and locals who fish.

Binkley et al. 1997. Status of Air Quality and Related Values in Class I National Parks and Monuments of the Colorado Plateau. Chapter 9. Grand Canyon National Park. National Park Service, Air Resources Division, Denver, CO. Available at https://irma.nps.gov/DataStore/Reference/Profile/585485

Eatough, D. J., Du, A., Joseph, J. M., Caka, F. M., Sun, B. J., Lewis, L., Mangelson, N. F., Eatough, M., Rees, L. B., Eatough, N. L., Farber, R. J., Watson, J. G. 1997. Regional source profiles of sources of SOx at the Grand Canyon during project MOHAVE. Journal of the Air & Waste Management Association 47(2): 101–118.

Eatough, D. J., Green, M., Moran, W., Farber, R. 2001. Potential particulate impacts at the Grand Canyon from northwestern Mexico. Science of the Total Environment 276 (1–3): 69–82.

Fenn, M. E., Haeuber, G. S., Tonnesen, J. S., Baron, J. S., Grossman-Clarke, S., Hope, D., Jaffe, D. A., Copeland, S., Geiser, L., Rueth, H. M., and Sickman, J. O. 2003. Nitrogen emissions, deposition and monitoring in the western United States. Bioscience 53: 391–403.

[GCVTC] Grand Canyon Visibility Transport Commission. 1996. Report of the Grand Canyon Visibility Transport Commission to the United States Environmental Protection Agency.

Green, M. C. 1999. The project MOHAVE tracer study: study design, data quality, and overview of results. Atmospheric Environment 33 (12): 1955–1968.

Green, M. C., Pitchford, M. L., Ashbaugh, L. 1996. Identification of candidate clean air corridors for the Colorado plateau. Journal of the Air & Waste Management Association 46 (5): 441–449.

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

Malm, W.C. and D.E. Day. 2001. Estimates of aerosol species scattering characteristics as a function of relative humidity. Atmospheric Environment 35: 2845-2860.

Malm, W., K. Gebhart, D. Latimer, T. Cahill, R. Eldred, A. Pielke, R. Stocker, and J. Watson. 1989. Winter Haze Intensive Tracer Experiment (WHITEX). Final report for the National Park Service. Fort Collins, CO.

[NPCA] National Parks Conservation Association. 2010. State of the Parks: Grand Canyon National Park. Resource Challenges and Future Directions. Washington, D.C. 84 pp.

[NPS] National Park Service. 1996. Baseline Water Quality Data Inventory and Analysis Grand Canyon National Park. NPS Technical Report NPS/NRWRD/NRTR—96/84. Washington, D.C. Available at https://irma.nps.gov/DataStore/Reference/Profile/2173779

Pitchford, M.L. and P.H. McMurry. 1994. Relationship between measured water vapor growth and chemistry of atmospheric aerosol for Grand Canyon, Arizona, in winter 1990. Atmospheric Environment. 28(5): 827-839.

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: Southern Colorado Plateau Network (SCPN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/330. National Park Service, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2168742

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., McPherson, G. T., McDonnell, T. C., Mackey, S. D., Moore, D. 2011d. Evaluation of the sensitivity of inventory and monitoring national parks to acidification effects from atmospheric sulfur and nitrogen deposition: Southern Colorado Plateau Network (SCPN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/360. National Park Service, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2170600

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