Part of a series of articles titled Park Air Profiles.
Air Quality at Denali National Park & Preserve
Most visitors expect clean air and clear views in parks. Denali National Park & Preserve (NP & Pres), Alaska, consistently has some of the best visibility and cleanest air of all national parks. Air quality monitoring in the park shows that the air in Denali NP & Pres is exceptionally clean on most days. During summer, however, it is not unusual for naturally-occurring smoke from wildland fires to significantly decrease visibility throughout Interior Alaska, including at the park. Concentrations of air pollutants, while low, show a strong seasonal trend, with peaks often occurring in the winter and early spring. This pattern is consistent with international transport of airborne contaminants to Alaska via transport pathways over the Arctic and Pacific Oceans (Wilcox 2001). The National Park Service works to address air pollution effects at Denali NP & Pres, and in parks across the U.S., through science, policy and planning, and by doing our part.
Nitrogen and Sulfur
Nitrogen and sulfur compounds deposited from the air may have harmful effects including acidification, on soils, lakes, ponds, and streams. 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). Nitrogen deposition exceeds the critical load for one or more park ecosystems (NPS ARD 2018).
The risk from either acidification or fertilization is considered low at Denali NP & Pres because rates of nitrogen and sulfur deposition are very low. However, certain vegetation communities in the park, including wetlands and arctic vegetation, are known to be vulnerable to excess nitrogen deposition. If nitrogen deposition increases significantly, these plant communities could be affected. Certain lichen species that occur in the park are known to be sensitive to air pollution, including the globally rare Erioderma pedicellatum (Nelson et al. 2009). Search for acid-sensitive plant species found at Denali NP & Pres.
Visit the NPS air quality conditions and trends website for park-specific nitrogen and sulfur deposition information. Denali NP & Pres has been monitoring nitrogen and sulfur deposition since 1980. Explore air monitoring »
Pollutants like mercury and pesticides are concerning because they are persistent and toxic in the environment. These contaminants can travel in the air thousands of miles away from the source of pollution, even depositing in protected places like national parks. In addition, while some of these harmful pollutants may be banned from use, historically contaminated sites continue to endure negative environmental consequences.
When deposited, airborne mercury and other toxic air contaminants are known to harm wildlife like birds and fish, and cause human health concerns. Many of 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 concentrations in fish varied between species and locations in Denali NP & Pres. Mercury concentrations in northern pike sampled from one site in the park did not exceed the toxicity thresholds for fish, birds, or US EPA’s human consumption guidance (Eagles-Smith et al. 2014). However, earlier work found that mercury concentrations in fish (lake trout, burbot, and whitefish) sampled from two different sites exceeded health thresholds for fish-eating birds (kingfishers) and mammals (otter and mink) (Ackerman et al. 2008; Landers et al. 2010; Landers et al. 2008; Schwindt et al. 2008). This underscores that the available data may not reflect the risk at other unsampled locations in the park. Fish consumption advisories may be in effect for mercury and other contaminants (NPS 2022).
- Some dragonfly larvae sampled from Denali NP&P had mercury concentrations at moderate impairment levels. Dragonfly larvae have been sampled and analyzed for mercury from four sites in the park; 50% of the data fall into the moderate (100-300 ng/g dw) impairment category for potential mercury risk. An index of moderate impairment or higher suggests some fish may exceed the US EPA benchmark for protection of human health (Eagles-Smith et al. 2020; Eagles-Smith et al. 2018).
- Contaminants and pesticides have been found in various samples from Denali. Lake-average dieldrin and/or p,p′-DDE (a degradation product of DDT often found in fish) concentrations in fish exceeded the human health threshold for subsistence fish consumption in some water bodies; also, historic-use contaminants were highest in Alaskan parks, as compared to the lower 48 states (Flanagan Pritz et al. 2014). Related studies found low levels of contaminants – including current-use pesticides, historic-use pesticides, and industrial by-products – in air, snow, sediment, fish, and vegetation (Hageman et al. 2006; Landers et al. 2010; Landers et al. 2008).
The NPS Air Resources Division reports on park conditions and trends for mercury. Visit the webpage to learn more.
Park vistas are sometimes 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.
Significant improvements in visibility on clearest days have been documented since the late 1980’s, and visibility in the park is quite close to the Clean Air Act goal of no human caused impairment. Haze-causing pollutants affecting Denali NP & Pres show a strong seasonal pattern, with a peak in the late winter and spring. The peak coincides with intercontinental transport of pollutants primarily from industrial sources, and can be seen throughout interior Alaska. In the summer, it is not uncommon for smoke from naturally-occurring wildland fires to obscure the view.
- Reduction of the average natural visual range from about 165 miles (without the effects of pollution) to about 160 miles because of pollution at the park
- Reduction of the visual range to below 105 miles on very hazy days
Visit the NPS air quality conditions and trends website for park-specific visibility information. Denali NP & Pres has been monitoring visibility since 1988. Check out the live air quality webcam and 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.
Ozone is a highly reactive molecule, and once inside a leaf, it 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 and seasonal exposures are generally low in Denali NP & Pres and unlikely to cause injury or reduced growth in plants.
Episodes of high ozone concentrations, due in part to biomass burning in Eurasia, have been documented in the park, but these episodes are relatively short in duration (Oltmans et al. 2010). While ozone effects have not been documented in the park, several park species, including Salix scouleriana (Scouler’s willow) and Populus tremuloides (quaking aspen), are known to be sensitive to ozone. Search additional ozone-sensitive plant species found at Denali NP & Pres.
Visit the NPS air quality conditions and trends website for park-specific ozone information. Denali NP & Pres has been monitoring ozone since 1987. Check out the live ozone and meteorology data from Denali NP & Pres and explore air monitoring »
Explore Other Park Air Profiles
There are 47 other Park Air Profiles covering parks across the United States and its territories.
Ackerman, L. K., Schwindt, A. R., Massey Simonich S. L., Koch, D. C., Blett, T. F., Schreck, C. B., Kent, M. L., Landers, D. H. 2008. Atmospherically Deposited PBDEs, Pesticides, PCBs, and PAHs in Western U.S. National Park Fish: Concentrations and Consumption Guidelines. Environmental Science & Technology 42: 2334–2341. https://irma.nps.gov/DataStore/Reference/Profile/652640
Eagles-Smith, C.A., J.J. Willacker, and C.M.Flanagan Pritz. 2014. Mercury in fishes from 21 national parks in the Western United States—Inter and intra-park variation in concentrations and ecological risk: U.S. Geological Survey Open-File Report 2014-1051, 54 p. Available at: http://dx.doi.org/10.3133/ofr20141051
Eagles-Smith, C.A., S.J. Nelson., C.M. Flanagan Pritz, J.J. Willacker Jr., and A. Klemmer. 2018. Total Mercury Concentrations in Dragonfly Larvae from U.S. National Parks (ver. 6.0, June 2021): U.S. Geological Survey data release. https://doi.org/10.5066/P9TK6NPT
Eagles-Smith, C.A., J.J. Willacker, S.J. Nelson, C.M. Flanagan Pritz, D.P. Krabbenhoft, C.Y. Chen, J.T. Ackerman, E.H. Campbell Grant, and D.S. Pilliod. 2020. Dragonflies as biosentinels of mercury availability in aquatic food webs of national parks throughout the United States. Environmental Science and Technology 54(14):8779-8790. https://doi.org/10.1021/acs.est.0c01255
Flanagan Pritz, C. M., J. E. Schrlau, S. L. Massey Simonich, T. F. Blett. 2014. Contaminants of Emerging Concern in Fish from Western U.S. and Alaskan National Parks – Spatial Distribution and Health Thresholds. Journal of American Water Resources Association 50 (2): 309–323. Available at https://irma.nps.gov/App/Reference/Profile/2210538.
Hageman, K. J., Simonich, S. L., Campbell, D. H., Wilson, G. R., Landers, D. H. 2006. Atmospheric deposition of current-use and historic-use pesticides in snow at national parks in the Western United States. Environmental Science & Technology 40: 3174–3180. https://irma.nps.gov/DataStore/Reference/Profile/648369
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. Available at https://pubs.acs.org/doi/10.1021/es901866e
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.
Nelson, P., Walton, J. and Roland, C. 2009. Erioderma pedicellatum (Hue) P. M. Jorg., New to the United States and Western North America, Discovered in Denali National Park and Preserve and Denali State Park, Alaska. Evansia 25: 19–23.
[NPS] National Park Service. 2022. Fish Consumption Advisories. https://www.nps.gov/subjects/fishing/fish-consumption-advisories.htm
Oltmans S. J., Lefohn, A. S., Harris, J. M., Tarasick, D. W., Thompson, A. M., Wernli, H., Johnson, B. J., Novelli, P. C., Montzka, S. A., Ray, J. D., Patrick, L. C., Sweeney, C., Jefferson, A., Dann, T., Davies, J., Shapiro, M., Holben, B. N. (In Press 2010). Enhanced ozone over western North America from biomass burning in Eurasia during April 2008 as seen in surface and profile observations. Atmospheric Environment.
Schwindt, A. R., Fournie, J. W., Landers, D. H., Schreck, C. B., Kent, M. 2008. Mercury Concentrations in Salmonids from Western U.S. National Parks and Relationships with Age and Macrophage Aggregates. Environmental Science & Technology 42 (4): 1365–1370. https://pubs.acs.org/doi/10.1021/es702337m
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: Central Alaska Network (CAKN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/330. National Park Service, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2168611
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: Central Alaska Network (CAKN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/349. National Park Service, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2170572
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.
Last updated: August 17, 2023