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Scenic views and native vegetation images from parks within Rocky Mountain Network

Air Pollution Impacts

Rocky Mountain National Park

Natural and scenic resources in Rocky Mountain National Park (NP) are susceptible to the harmful effects of air pollution. Nitrogen, pesticides, ozone, and fine particles impact natural resources including surface water, wildlife, and vegetation, and scenic resources such as visibility. These resources may be affected by air pollutants like ozone, nitrogen, pesticides, and fine particles. Click on the tabs below to learn more about air pollutants and their impacts on natural and scenic resources at Rocky Mountain NP.

  • Nitrogen
  • Toxics
  • Ozone
  • Visibility

Nitrogen Critical Load Development

Increased amounts of atmospheric nitrogen (N) deposition from rain and snow—known as “wet” deposition—at Rocky Mountain NP have resulted in an N wet deposition rate of approximately 3.1 kilograms per hectare per year (kg/ha/yr), as compared to the natural background at 0.2 kg/ha/yr. Scientists determined that changes to alpine lake aquatic communities at the park began in the 1950s, when N wet deposition rates were about 1.5 kg/ha/yr—a threshold defined as the “critical load” (Baron 2006). The critical load represents a threshold below which significant harmful effects to sensitive ecosystems components are not likely to occur. Efforts to reduce N deposition at the park have used the N critical load to establish goals for ecosystem recovery. N deposition has caused a variety of effects (graph [pdf, 95 KB]) to other park ecosystems as well.

Nitrogen compounds deposited from the air to lakes, streams, soils, and vegetation at Rocky Mountain NP are a threat to aquatic and terrestrial resources. High elevation ecosystems at the park are particularly vulnerable to nitrogen deposition. Not only do these systems receive more deposition than lower elevation areas, but short growing seasons and shallow soils allow a greater availability of nitrogen in the ecosystem.

Effects of nitrogen deposition at Rocky Mountain NP include:

  • Nitrogen saturation of soils in high-elevation watersheds. Excess nitrogen leaks from the soils into lakes and streams, altering water chemistry (Baron et al. 2000).
  • Alteration of aquatic communities in alpine lakes, with changes in the amounts and types of microscopic organisms called diatoms (Wolfe et al. 2001; research summary [pdf, 105 KB]).
  • Stimulation of soil microbial activity, resulting in increased mineralization and nitrification, processes that create more available nitrogen; and elevated nitrogen in spruce needles, potentially causing greater susceptibility to forest disease, drought, or insect infestations (Rueth et al. 2002; research summary [pdf, 641 KB]).
  • Unnatural fertilization of alpine plant communities, placing them at the threshold of shifting from forbs—such as showy wildflowers—to increased grasses.
  • Increased nitrogen concentrations in lichens, organisms that grow on trees and rocks (Landers et al. 2008; Landers et al. 2010).

Additional Information:

loch vale outlet, rocky mountain national park
High elevation surface waters at Rocky Mountain NP, Colorado, such as Loch Vale, are susceptible to nitrogen deposition.
  • Overview fact sheet (pdf, 214 KB)
  • Explore an interactive tutorial to understand how nitrogen cycles through our environment, from sources of nitrogen, transport through the atmosphere, and effects on the environment.
  • Watch a video to understand how animal agriculture contributes to nitrogen deposition at Rocky Mountain NP.
  • Read background information (pdf, 641 KB) about the issues and effects of nitrogen deposition in the Rocky Mountain NP.
  • Examine how agricultural best management practices (pdf, 475 KB) can be used to help reduce nitrogen impacts at Rocky Mountain NP.

Get Nitrogen & Sulfur Data  »


Photo of a fish at Spirit Lake in Rocky Mountain NP, Colorado
Some fish at Rocky Mountain NP, Colorado, have elevated levels of contaminants.

Toxic air pollutants include a suite of airborne contaminants such as pesticides, industrial by-products, heavy metals, and emerging chemicals such as flame retardants for fabrics. Certain airborne contaminants are known or suspected to cause cancer or other serious health effects in humans and wildlife, including reproductive problems, impaired growth and development, behavioral abnormalities, and reduced immune response.

Effects of airborne toxics on ecosystems at Rocky Mountain NP include:

  • Concentrations of dieldrin (a historic-use pesticide) in fish that exceed human health risk thresholds, and concentrations of current-use pesticides (e.g., endosulfans and dacthal) in fish higher than in other western U.S. national parks.
  • Currently used agricultural and industrial contaminants (e.g., flame retardants, PBDEs) detected in fish and sediment. Lake sediment records indicate that PBDEs are increasing rapidly in park ecosystems, but concentrations in fish remain below human or wildlife health consumption thresholds.
  • Elevated concentrations of mercury in snow, rain, and sediment as compared to other western U.S. national parks.
  • Contaminants such as pesticides generally higher on the park’s east side as compared to the west side.
  • Male “intersex” fish (the presence of both male and female reproductive structures in the same fish) found in the park, a response that often indicates exposure to contaminants.
  •    (Source: Landers et al. 2008; Landers et al. 2010)

Get Toxics Data  »


Photo of An NPS Biologist examining Cone flowers for ozone damage. Rocky Mountin NP, Colorado
An NPS Biologist examines coneflower leaves for ozone damage. Rocky Mountain NP, Colorado

Naturally-occurring ozone in the upper atmosphere forms a layer that absorbs the sun’s harmful ultraviolet rays and protects all life on earth. However, in the lower atmosphere, ozone is an air pollutant, forming when nitrogen oxides from vehicles, power plants, and other sources combine with volatile organic compounds from gasoline, solvents, and vegetation in the presence of sunlight. In addition to inducing respiratory problems in people, elevated ozone exposures can injure plants, evident either as visible injury to leaves or, although difficult to measure in a natural setting, as reduced growth and reproduction.

Effects of ozone on vegetation at Rocky Mountain NP include:

  • Visible injury to leaves, including “black fleck” on cut-leaf coneflowers, a result of the uptake of ozone by leaf pores (stomata) and subsequent cell tissue death (research summary [pdf, 98 KB]).

Search the list of ozone-sensitive plant species (pdf, 184 KB) found at each national park!

Ozone and Public Health Concern

Ground-level ozone concentrations at Rocky Mountain NP sometimes exceed the National Ambient Air Quality Standards set by the U.S. Environmental Protection Agency to protect public health. Park managers have instituted an ozone advisory program to educate employees and park visitors about the risks of exposure to unhealthy ozone levels and precautions that can be taken.

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. Park managers are optimistic that ozone air quality will improve at Rocky Mountain NP because of recent air quality regulations and other related actions.

Get Ozone Data  »


Many visitors come to parks to enjoy the spectacular vistas. Unfortunately, these vistas are sometimes obscured by fine particles of pollution in the atmosphere that create haze. Many of the same pollutants that ultimately fall out as nitrogen and sulfur deposition cause haze and impair visibility while suspended in the air. Organic compounds, soot, and dust reduce visibility as well.

Visibility effects at Rocky Mountain NP include:

  • Reduction of the average natural visual range from about 160 miles (without the effects of pollution) to about 110 miles because of pollution at the park.
  • Reduction of the visual range in the summer from about 80 miles to below 40 miles on high pollution days.
  • Impairment of visibility to some degree most of the time at the park.
  •    (Source: Copeland et al. 2008; EPA 2003; IMPROVE 2010)

Good and Poor visibility of Longs Peak, Rocky Mountain National Park, Colorado
Good (left) and poor (right) visibility of Longs Peak, Rocky Mountain NP, Colorado

Explore scenic vistas through three live webcams at Rocky Mountain National Park!

Get Visibility Data » 


Featured Content

Studies and Monitoring icon

Studies and monitoring help the NPS understand the environmental impacts of air pollution. Access air quality data and see what is happening with Studies and Monitoring at Rocky Mountain NP.

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Last Updated: December 30, 2016