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Studies and Monitoring

Grand Canyon National Park

Grand Canyon National Park (NP), Arizona, has its own unique environmental concerns based on its particular ecology. Air quality studies and monitoring programs at Grand Canyon NP focus on visibility, nitrogen and sulfur deposition, ozone, and toxic contaminants such as mercury. Click on the tabs below to review air quality studies and key scientific references at Grand Canyon NP, as well as to access information on air quality monitoring in the park.

  • Studies & Projects
  • Monitoring & Data
  • Key References

Ongoing research in Grand Canyon NP, Arizona:

Clearing the Air at Grand Canyon NP

The pollutants that affect air quality at Grand Canyon can come from both near and distant sources. The U.S. Clean Air Act, amended in 1990, recognized this and mandated the establishment of the Grand Canyon Visibility Transport Commission (GCVTC) to study the interstate transport of air pollutants into the region. Visibility assessments in the park followed (MOHAVE, WHITEX). In 1996, the Commission’s recommendations to the Environmental Protection Agency included reducing air pollution emissions from industry and vehicles (GCVTC 1996 [pdf, 1.5 MB]). The recommendations were aimed at protecting clear days and reducing dirty days at national parks and wilderness areas. These goals would be achieved through changed energy policies and improved control technologies, and reducing smoke from forest fires and agricultural burning (Green et al. 1996). The Western Regional Air Partnership (WRAP), a voluntary organization of Western states, tribes, and federal agencies, is the successor to the Grand Canyon Visibility Transport Commission. WRAP works to implement the recommendations of the GCVTC and develop new technical and policy tools to assist Western states in complying with Environmental Protection Agency haze regulations. Other federal agencies involved include Bureau of Land Management, Fish & Wildlife Service, U.S. Forest Service, and the National Park Service.

Visibility Impacts

Many visitors only experience the Grand Canyon NP from the vantage point of the rims, and therefore clean, clear air is essential for visitors to enjoy views of the park (NPCA 2010). Visibility impact studies over the past couple decades explored fine particle contributions to haze, local, and regional emission sources, wind trajectories to the park, and more. Most of the fine particles affecting the park travel long distances from urban and industrial areas, mixing en route to form a uniform “regional haze” that obscures scenic vistas. In-park sources, with the exception of forest fires, make a very minor contribution to fine particle levels at the park (GCVTC 1996; Green et al. 1996; Eatough et al. 1997; Green 1999; Eatough et al. 2001).

Ground-Level Ozone Impacts

Grand Canyon NP has monitored ozone concentrations on the South Rim continuously since 1989. Dry conditions typical of the park cause plants to close their stomata to conserve water, limiting ozone uptake and subsequent injury. However, plants in riparian areas 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. Higher nighttime ozone levels may increase damage potential for drought-adapted plant species that respire at night. Field surveys on ponderosa pine in 1992–1993 and 2008 did not observe any ozone injury (Binkley et al. 1997; NPCA 2010 [pdf, 11.8 MB]).

Air quality monitoring information and data access:

Air Pollutant/Impact

Monitoring Program

Sites and Data Access

Visibility IMPROVE
Nitrogen & Sulfur Wet deposition NADP/NTN
Dry deposition CASTNet

Abbreviations in the above table:

    ASTNet: EPA Clean Air Status and Trends Network
    GPMP: Gaseous Pollutant Monitoring Program
    IMPROVE: Interagency Monitoring of Protected Visual Environments
    NADP: National Atmospheric Deposition Program
    NPS: National Park Service
    NTN: National Trends Network
    VIEWS: Visibility Information Exchange Web System

For more information regarding monitoring and data assessments conducted by the National Park Service, link to the NPS Air Quality Monitoring Program or to the NPS Air Quality Monitoring History Database for a history of active and inactive monitoring sites at Grand Canyon NP.

Key air quality related references from Grand Canyon NP, Arizona:

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 (pdf, 686 KB).

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. Available at (pdf, 1.5 MB).

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.

[IMPROVE] Interagency Monitoring of Protected Visual Environments. 2010. Improve Summary Data. Available at

[NPCA] National Parks Conservation Association. 2010. State of the Parks: Grand Canyon National Park. Resource Challenges and Future Directions. Washington, D.C. 84 pp. Available at (pdf, 11.8 MB).

[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 (pdf, 12.4 MB).

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

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 (pdf, 7.4 MB).

Featured Content

Impacts icon

Pollutants including fine particles, nitrogen, sulfur, ozone, and mercury affect resources such as streams, soils, and scenic vistas. Find out how on our Grand Canyon NP Air Pollution Impacts web page.

Related Links

Last Updated: June 14, 2011