For more information about National Park Service air resources, please visit

Scenic views and native vegetation images from parks within North Coast and Cascades Network

Air Pollution Impacts

North Cascades National Park

Natural and scenic resources in North Cascades National Park (NP) are susceptible to the harmful effects of air pollution. Nitrogen, toxics, ozone, and fine particles impact natural resources such as lakes, streams, fish, and vegetation, and scenic resources such as visibility. Click on the tabs below to learn more about air pollutants and their impacts on natural and scenic resources at North Cascades NP.

  • Nitrogen & Sulfur
  • Toxics & Mercury
  • Ozone
  • Visibility

How much nitrogen is too much?

Nitrogen is a fertilizer and some nitrogen is necessary for plants to grow. However, in natural ecosystems, too much nitrogen disrupts the balance of plant and aquatic communities, allowing weed species to grow faster. In some areas of Washington State, including the Columbia River Gorge and the Willamette Valley, high levels of nitrogen deposition have changed lichen communities. In those areas, lichens adapted to low nitrogen conditions are being replaced by lichens adapted to a more disturbed, polluted environment (Geiser and Neitlich 2007; Geiser et al. 2010). A survey at North Cascades NP found that current levels of nitrogen deposition are low and impacts to the lichen community have not been observed. However, lichens may provide an early warning system if nitrogen deposition increases. Similarly, the composition of sensitive aquatic communities can provide an early warning system on nitrogen deposition effects to waterbodies.

Nitrogen and sulfur compounds deposited from air pollution may harm lakes, streams, soils, and vegetation in North Cascades NP. The largest regional sources of nitrogen and sulfur include agriculture, refineries, aluminum smelters, and automobiles. Certain high elevation ecosystems in the park are highly sensitive to over-enrichment or acidification from nitrogen and sulfur deposition. For example, short growing seasons and shallow soils at high elevations limit the capacity of soils and plants to absorb nitrogen. Excess nitrogen can result in soil nutrient imbalances and changes in alpine plant communities. And, while lakes and streams receiving base cation-enriched glacial melt are buffered from the acidifying effects of sulfur and nitrogen deposition, other more dilute, high elevation surface waters not receiving glacial melt are sensitive to acidification.

Photo of McAlester Lake at North Cascades NP in Washington.
Some high elevation lakes at North Cascades NP, Washington, are particularly sensitive to acid inputs from sulfur and nitrogen deposition.

Effects of sulfur and nitrogen deposition at North Cascades NP include:

  • Higher inorganic nitrogen deposition and slightly higher surface-water nitrate concentrations relative to Mount Rainier NP (Clow and Campbell 2008 [pdf, 2.12 MB]);
  • Spring snowmelt, late summer storms, or rain-on-snow events can release accumulated acids in snow to streams and lakes, with potentially detrimental effects on fish, aquatic insects, and amphibians (Clow and Campbell 2008 [pdf, 2.12 MB]);
  • Increased nitrate concentrations in alpine lakes as elevation increases, suggesting that atmospheric deposition contributes to the increasing levels of nitrogen in high elevation lakes (Larson et al. 1999);
  • In addition to vehicles, power plants and industry, nearby agricultural sources contribute to nitrogen deposition in the park (Basabe et al. 1989a).

Get Sulfur & Nitrogen Data »


Photo of a Douglas fir at North Cascades NP in Washington
Studies found elevated levels of pesticides on conifer needles and in other ecosystem indicators (e.g. fish, air) at North Cascades NP, Washington.

Toxics, including heavy metals like mercury, accumulate in the tissue of organisms and may alter key ecosystem processes. When mercury converts to methylmercury in the environment and enters the food chain, effects can include reduced reproductive success, impaired growth and development, behavioral abnormalities, reduced immune response, and decreased survival. Human activities have greatly increased the amount of mercury in the environment through processes such as burning coal for electricity and burning waste. Other toxic air contaminants of concern include pesticides, industrial by-products, and emerging chemicals. Some of these toxics are also known or suspected to cause cancer or other serious chronic health effects in humans and wildlife.

Effects of mercury and airborne toxics on ecosystems at North Cascades NP include:

  • Contaminant accumulation including mercury, current-use pesticides, historic-use pesticides, and industrial by-products in air, vegetation, and fish (Moran et al. 2007; Landers et al. 2010; Landers et al. 2008);
  • Fish from “contaminated” lakes (i.e., elevated mercury, DDE, and PCBs) in Washington’s high elevation national parks including North Cascades NP, have altered metabolic, endocrine, and immune response-related genes, as compared to fish from uncontaminated lakes (Moran et al. 2007);
  • Elevated concentrations of current-use pesticides (chlorpyrifos, endosulfans, dacthal, and lindane) found in park vegetation (Landers et al. 2010; Landers et al. 2008);
  • Elevated levels of current use pesticides and other toxic air contaminants in air and vegetation samples as compared to other national parks studied (Landers et al. 2010; Landers et al. 2008).

Get Toxics Data »


Photo of Virginia creeper (Parthenocissus quinquefolia) at North Cascades NP in Washington.
Virginia creeper, a species sensitive to ozone injury at North Cascades NP, Washington.

Naturally-occurring ozone in the upper atmosphere absorbs the sun’s harmful ultraviolet rays and helps to protect 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 causing respiratory problems in people, ozone can injure plants. Ozone enters leaves through pores (stomata), where it can kill plant tissues, causing visible injury, or reduce photosynthesis, growth, and reproduction.

Ozone is transported to the park from the Puget Sound urban zone and trans-Pacific sources (Eilers et al. 1994 [pdf, 520 KB]; Barna et al. 2000; Jaffe et al. 2003). However, ozone concentrations in the region are generally low, and ozone injury to plants in the park has not been evaluated. Nevertheless, several species, including Pinus ponderosa (ponderosa pine) and Populus tremuloides (quaking aspen), are known to be sensitive to ozone.

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

Get Ozone Data »


Three images depicting air quality impacts on visibility at North Cascades National Park, Washington (clear to hazy from top to bottom).
Air pollutants can affect visibility at North Cascades NP, Washington (clear to hazy from top to bottom).

Many visitors come to North Cascades NP to enjoy views of the “American Alps,” including jagged spires, sheer cliffs, and glaciers. Unfortunately, these vistas are often obscured by haze caused by fine particles in the air. Many of the same pollutants that ultimately fall out as nitrogen and sulfur deposition contribute to this haze and visibility impairment. Organic compounds, soot, and dust reduce visibility as well.

Visibility effects at North Cascades NP include:

  • Reduction of the average natural visual range from about 150 miles (without the effects of pollution) to about 90 miles because of pollution at the park;
  • Reduction of the visual range from about 105 miles to below 50 miles on high pollution days;
  • Human caused haze sometimes impairs scenic vistas at the park.

(Source: IMPROVE 2010)

Additional Information:

  • Explore scenic vistas through a live webcam at North Cascades National Park!
  • Learn about PREVENT, the Pacific Northwest Regional Visibility Experiment Using Natural Tracers special study. This 1990 study investigated the contribution of emission sources to fine particle concentrations and regional haze. more »

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 North Cascades NP.

Related Links

Last Updated: December 30, 2016