Air Quality

The air in Denali National Park is exceptionally clean, allowing spectacular views of the Alaska Range when the mountains are free of clouds. National Park Service air quality monitoring has shown that Denali consistently has some of the best visibility and cleanest air measured in the country, although parks in the Pacific Northwest often record lower annual ozone values, and western desert parks sometimes have fewer visibility-degrading particles in the air. It is not surprising to discover that Alaska has such clean air, considering the low population density and relatively sparse industrial activity in the state.

What may be surprising, however, is the presence of airborne contaminants in Denali that travel halfway around the world before reaching the park. Each year, small but measurable amounts of pollution arrive in Denali from Europe and Asia. These persistent pollutants come from power plants, metal smelters, and other industrial sources, and are transported over the North Pole and throughout the arctic regions in a phenomenon called arctic haze. Desert dust and agricultural contaminants can travel directly across the Pacific Ocean to reach the park. Airborne contaminants from other continents will likely increase over time as the source areas grow and develop. Denali’s clean air may eventually depend more on international treaties and the environmental policies of other countries than on U.S. laws designed to protect air quality.

Under the U.S. Clean Air Act, Denali receives the strongest protection possible as a designated Class I area. The National Park Service carries out its responsibility to protect park air quality in the following ways:
  • Communicating information about air quality in parks to the public
  • Providing recommendations and technical assistance to state, federal and tribal regulatory agencies
  • Working cooperatively through partnerships in the development of air pollution control strategies
  • Promoting sustainability and pollution prevention practices in parks
The National Park Service Air Resources Program offers more information on pollutants in national parks.

Persistent Organic Pollutants

Although Denali’s ecosystems are as intact as any in North America, and the scenery is breathtaking, these protected lands and waters are not as pristine as they may seem. Toxic airborne contaminants are accumulating in the arctic regions of the world, and Denali is no exception. DDT, the toxic chemical Rachel Carson warned about in her classic book, Silent Spring, is present in the sediments of Wonder Lake in concentrations among the highest measured in remote arctic lakes and rivers. DDT is one of many compounds classified as Persistent Organic Pollutants, or POPs, that are toxic to animals, including humans, and break down very slowly in the environment.

POPs can cause cancer, organ failure, and endocrine disruption, and other health effects, though it may take years of exposure for symptoms to be expressed. In the body, they are stored in fatty tissues, accumulating throughout an individual’s lifetime, and can become more concentrated at the upper levels of food chains through a process called bioaccumulation.

Arctic and subarctic ecosystems like Denali’s are particularly susceptible to accumulating POPs and other toxic airborne contaminants. In warmer climates, POPs are transported into an area, deposited from the atmosphere, and revolatilized back into the air. In colder parts of the world such as Denali, POPs are steadily deposited, but revolatilization is slower, so more contaminants remain in the ecosystem. Over time, this can lead to significant accumulation of POPs and other toxic airborne contaminants.

The National Park Service is embarking on a 5-year assessment program to determine the extent of POPs in Denali and six other national parks. You can find out more about this program, POPs, and other toxic airborne contaminants at the following web sites:

UV and Ozone

Ultraviolet radiation (UV) and ozone was monitored at Denali as part of a network of fourteen national parks established to understand the effects of UV radiation at both local and global scales. Although UV is a natural form of radiation, humans and ecosystems are being exposed to high levels of UV as the earth’s ozone layer is depleted. Ozone high in the stratosphere filters out UV radiation, but this layer is being jeopardized by man-made pollutants, chlorofluorocarbons (CFCs) and related compounds, that destroy the ozone molecules. Despite international treaties to phase out the use of CFCs and other ozone depleting chemicals, these chemicals persist in the upper atmosphere and continue to damage our UV shield.

Seasonal "ozone holes", where the ozone layer is particularly thin, are greater at higher latitudes. Denali National Park is well positioned as a site for measuring changes in UV radiation and ozone at high latitudes.The UV monitoring at Denali will help scientists determine if there are changes in incoming ultraviolet radiation that may be affecting human health and ecosystem processes.

UV radiation was measured by a Brewer spectrophotometer located at park headquarters on the east side of Denali Park. This sophisticated instrument tracked the sun and monitored the variation in solar radiation throughout the day. It also recorded data on atmospheric ozone and gas concentrations that were then used to calculate the amount of UV at the surface of the earth.