Park Air Profiles - Sequoia & Kings Canyon National Parks

Air Quality at Sequoia & Kings Canyon National Parks

Most visitors expect clean air and clear views in parks. Sequoia & Kings Canyon National Parks (NPs), in California, are home to huge mountains, rugged foothills, deep canyons, vast caverns, and the world's largest trees. The parks also experience some of the worst air pollution of any of the national parks in the U.S. The parks are downwind from many air pollution sources, including agriculture, industry, major highways, and urban pollutants from as far away as the San Francisco Bay Area. Air pollutants blown into the park can harm natural and scenic resources such as soils, surface waters, plants, wildlife, and visibility. The National Park Service works to address air pollution effects at Sequoia & Kings Canyon NPs, and in parks across the U.S., through science, policy and planning, and by doing our part.

Nitrogen and Sulfur

Hiker on a trail
Visitors come to Sequoia & Kings Canyon NPs to view mountains and canyons and hike wilderness trails.

Nitrogen (N) and sulfur (S) compounds deposited from the air may have harmful effects on ecosystem processes. Healthy ecosystems can naturally buffer a certain amount of pollution, but once a threshold is passed the ecosystem may respond negatively. This threshold is the critical load, or the amount of pollution above which harmful changes in sensitive ecosystems occur (Porter 2005). N and S deposition change ecosystems through eutrophication (N deposition) and acidification (N + S deposition). Eutrophication increases soil and water nutrients which causes some species to grow more quickly and changes community composition. Ecosystem sensitivity to nutrient N enrichment at Sequoia National Park (SEQU) and Kings Canyon National Park (KICA) relative to other national parks is very high (Sullivan et al. 2016); for a full list of N sensitive ecosystem components, see: NPS ARD 2019. Acidification leaches important cations from soils, lakes, ponds, and streams which decreases habitat quality. Ecosystem sensitivity to acidification at SEQU and KICA relative to other national parks is very high (Sullivan et al. 2016); to search for acid-sensitive plant species, see: NPSpecies.

From 2017-2019 total N deposition in SEQU and KICA ranged from 4.3 to 8.6 kg-N ha-1 yr-1 and total S deposition ranged from 0.9 to 1.9 kg-S ha-1 yr-1 based on the TDep model (NADP, 2018). SEQU and KICA have been monitoring atmospheric N and S deposition since 1980, see the conditions and trends website for park-specific information.

Some high elevation ecosystems in SEQU and KICA have shown variable response to N. These systems receive more N deposition than lower elevation areas and short growing seasons and shallow soils limit the capacity of soils and plants to absorb N. Sources of N in the parks include the Central Valley and San Francisco Bay Area (LeNoir et al. 1999; Bytnerowicz et al. 2002; Hageman et al. 2006).

Additional N Research:
  • Increased plant growth in lakes from nutrient enrichment, potentially changing aquatic community dynamics (Sickman et al. 2003)
  • Replacement of certain lichen species important for wildlife food and habitat by weedy, nitrogen-loving species (Fenn et al. 2008)
  • Episodic acidification of some streams during snowmelt (Williams and Melack 1991; Stoddard 1995; Leydecker et al. 1999)

Alpine ecosystem effects

Alpine environments are particularly vulnerable to large inputs of reactive nitrogen because of the sparse cover of vegetation, short growing seasons, large areas of exposed bedrock and talus, and snowmelt nutrient releases (Williams et al., 1996; Nanus et al., 2012). Approximately 57% of the land area in SEQU and KICA is alpine (~328 km2 above 1550 m). McClung et al. (2021) compared the 2015 estimated total N deposition (TDep; NADP, 2018) to the critical load of N for an increase in alpine sedge growth (alpine plant critical load = 3 kg-N ha-1yr-1) and the critical load of N for alpine soil nitrate leaching (alpine soil critical load = 10 kg-N ha-1yr-1; Bowman et al., 2012). They found that deposition exceeded the alpine plant critical load in 5.9% of the park’s alpine area, but was below the alpine soil critical load throughout the park’s entire alpine area.

Epiphytic macrolichen community responses

Epiphytic macrolichens grow on tree trunks, branches, and boles. Since these lichens grow above the ground, they obtain all their nutrients directly from precipitation and the air. Many epiphytic lichen species have narrow environmental niches and are extremely sensitive to changes in air pollution. Geiser et al. (2019) used a U.S. Forest Service national survey to develop critical loads of nitrogen (N) and critical loads of sulfur (S) to prevent more than a 20% decline in four lichen community metrics: total species richness, pollution sensitive species richness, forage lichen abundance, and cyanolichen abundance.

McCoy et al. (2021) used forested area from the National Land Cover Database to estimate the impact of air pollution on epiphytic lichen communities. Forested area makes up 734 km2 (20.9%) of the land area of Sequoia National Park and Kings Canyon National Park.

  • N deposition exceeded the 3.1 kg-N ha-1 yr-1 critical load to protect N-sensitive lichen species richness in 57.8% of the forested area.
  • S deposition was below the 2.7 kg-S ha-1 yr-1 critical load to protect S-sensitive lichen species richness in every part of the forested area.

For exceedances of other lichen metrics and the predicted decline of lichen communities see Appendices A and B of McCoy et al. (2021).

Additional modeling was done on 459 lichen species to test the combined effects of air pollution and climate gradients (Geiser et al. 2021). A critical load indicative of initial shifts from pollution-sensitive toward pollution-tolerant species occurred at 1.5 kg-N ha-1 yr-1 and 2.7 kg-S ha-1 yr-1 even under changing climate regimes.

Plant species response

Plants vary in their tolerance of eutrophication and acidification, and some plant species respond to nitrogen (N) or sulfur (S) pollution with declines in growth, survival, or abundance on the landscape. Horn et al. (2018) used the U.S. Forest Service national forest survey to develop critical loads of N and critical loads of S to prevent declines in growth or survival of sensitive tree species. Clark et al. (2019) used a database of plant community surveys to develop critical loads of N and critical loads of S to prevent a decline in abundance of sensitive herbaceous plant species. According to NPSpecies, Sequoia National Park and Kings Canyon National Park contain:

  • 4 N-sensitive tree species and 21 N-sensitive herbaceous species.
  • 6 S-sensitive tree species and 17 S-sensitive herbaceous species.

Change in N and S deposition from 2000 to 2021

The maps below show how the spatial distribution of estimated Total N and Total S deposition in SEKI has changed from 2000-2002 to 2019-2021 (TDep MMF version 2022.02). Slide the arrows in the middle of the image up and down to compare N and S deposition between the two years (Yearly Data).

  • Minimum N deposition decreased from 4.6 to 3.3 kg-N ha-1 yr-1 and maximum N deposition decreased from 14.9 to 14.7 kg-N ha-1 yr-1.
  • Minimum S deposition decreased from 0.8 to 0.7 kg-S ha-1 yr-1 and maximum S deposition decreased from 2.1 to 1.5 kg-S ha-1 yr-1.
Two maps showing SEKI boundaries. The left map shows the spatial distribution of estimated total nitrogen deposition levels from 2000-2002. The right map shows the spatial distribution of estimated total sulfur deposition levels from 2000-2002. Two maps showing SEKI boundaries. The left map shows the spatial distribution of estimated total nitrogen deposition levels from 2000-2002. The right map shows the spatial distribution of estimated total sulfur deposition levels from 2000-2002.

Estimated total nitrogen and sulfur deposition levels from 2000-2002 (top) compared to the 2019-2021 (bottom) average at SEKI. Estimated values were developed using the National Atmospheric Deposition Program - Total Deposition (TDep) approach that combines measured and modeled data. Estimated values are valuable for analyzing gradients of deposition and the resulting ecosystem risks where monitors are not present.

Persistent Pollutants

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.

The NPS Air Resources Division reports on park conditions and trends for mercury. Visit the webpage to learn more.


View of Big Baldy from Redwood Canyon
Clean, clear air is essential to appreciating the scenic vistas at Sequoia & Kings Canyon NPs.

Many visitors come to enjoy the spectacular vistas found at Sequoia & Kings Canyon NPs. Distant vistas are often obscured by haze, reducing how well and how far people can see. Visibility reducing haze is caused by tiny particles in the air (see particulate matter below). Many of the same pollutants that ultimately fall out as nitrogen and sulfur deposition contribute to this haze. Organic compounds, soot, dust, and wood smoke reduce visibility as well. Significant improvements in park visibility on clearest days as well as haziest days have been documented since the 1990’s. Still, visibility in the park is a long way from the Clean Air Act goal of no human caused impairment.

Visibility effects:

  • Reduction of the average natural visual range from about 150 miles (without the effects of pollution) to about 65 miles because of pollution at the parks
  • Reduction of the visual range from about 115 miles to below 30 miles on high pollution days

Visit the NPS air quality conditions and trends website for park-specific visibility information. Sequoia & Kings Canyon NPs have been monitoring visibility since 1992. View a live air quality webcam and explore air monitoring »

Ground-Level Ozone

Ponderosa Pine Tree
Ponderosa pine trees are one of the ozone sensitive species found at Sequoia & Kings Canyon NPs.

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.

During the summer months, ozone levels in the park frequently exceed the National Ambient Air Quality Standards set by the U.S. Environmental Protection Agency to protect public health. 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. When ozone levels exceed, or are predicted to exceed, health standards, Sequoia & Kings Canyon NPs staff post health advisories cautioning staff and visitors of the potential health risks associated with exposures to elevated levels.

Over the course of a growing season, ozone can also 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. Some plants are more sensitive to ozone than others. Search ozone-sensitive plant species found at Sequoia & Kings Canyon NPs.

Ozone effects:

  • Widespread and severe injury to Ponderosa and Jeffrey pines in the parks (Arbaugh et al. 1998).
  • Injury to ponderosa pine and Jeffrey pine needles (Warner et al. 1983), with ozone injury evident on nearly 90% of Jeffrey pines in or near the Giant Forest on the west side of the parks where ozone exposure is highest (Peterson et al. 1991; Peterson and Arbaugh 1992);
  • Reduced tree health and growth in some locations due to chronic, long-term ozone exposure (Peterson et al. 1987; Ewell et al. 1989; Peterson et al. 1991; Duriscoe and Stolte 1992; Peterson and Arbaugh 1992);
  • Injury to Giant Sequoia seedlings, possibly affecting their long-term success (Grulke and Miller 1994; Miller and Grulke 1994).

Visit the NPS air quality conditions and trends website for park-specific ozone information. Sequoia & Kings Canyon NPs have been monitoring ozone since 1984. View live ozone and meteorology data, and explore air monitoring »

Particulate Matter

Concentrations of fine particles in the air at Sequoia and Kings Canyon NPs sometimes exceed the National Ambient Air Quality Standards set by the U.S. Environmental Protection Agency to protect human health. Fine particles (smaller than 2.5 micrometers) originate from either direct emissions by a source, such as construction sites, power plants, and fires, or reactions with gases and aerosols in the atmosphere emitted from pollution sources upwind.

Because of their small size, fine particles can get deep into the lungs and cause serious health problems. Numerous scientific studies have linked particle pollution exposure to irritation of the airways, coughing, difficulty breathing, aggravated asthma, chronic bronchitis, heart attacks, and premature death in people with heart or lung disease.

Sequoia & Kings Canyon NPs have been monitoring particulate matter since 1992. Check out the most recent particulate matter levels on our live data site and explore air monitoring »

Explore Other Park Air Profiles

There are 46 other Park Air Profiles covering parks across the United States and its territories.


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Part of a series of articles titled Park Air Profiles.

Sequoia & Kings Canyon National Parks

Last updated: August 17, 2023