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Park Air Profiles - Redwood National and State Parks

Air Quality at Redwood National and State Parks

Most visitors expect clean air and clear views in parks. Redwood National and State Park (NSP), California, home to the world’s tallest trees, is upwind from many pollution sources. Still, emissions from nearby logging and mining operations, wood smoke, vehicles, power plants, and agriculture can harm the park’s natural and scenic resources such as, surface waters, plants, and visibility. The National Park Service works to address air pollution effects at Redwood NSP, and in parks across the U.S., through science, policy and planning, and by doing our part.

Nitrogen and Sulfur

Visitor in a wheelchair on a trail in Redwood NSP
Visitors come to Redwood NSP to enjoy scenic views of the California coastline, river-ways, and the tallest trees on Earth.

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 Redwood National Park (REDW) relative to other national parks is very low (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 REDW relative to other national parks is high (Sullivan et al. 2016); to search for acid-sensitive plant species, see: NPSpecies.

From 2017-2019 total N deposition in REDW ranged from 3.7 to 5.2 kg-N ha-1 yr-1 and total S deposition ranged from 1.2 to 1.8 kg-S ha-1 yr-1 based on the TDep model (NADP, 2018). See the conditions and trends website for park-specific information on N and S deposition at REDW.

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 485 km2 (84.5%) of the land area of Redwood National Park.

  • N deposition exceeded the 3.1 kg-N ha-1 yr-1 critical load to protect N-sensitive lichen species richness in 100% 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, Redwood National Park contains:

  • 6 N-sensitive tree species and 17 N-sensitive herbaceous species.
  • 8 S-sensitive tree species and 14 S-sensitive herbaceous species.

Visibility

View of shore at Redwood NSP
Clean, clear air is essential to appreciating the scenic vistas at Redwood NSP.

Many visitors come to Redwood NSP to enjoy views of primeval redwood forests against the rugged coastline of the Pacific Ocean. 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, dust, and wood smoke reduce visibility as well. Naturally-occurring marine fog, which also limits visibility at the park, provides necessary water to the moisture-loving redwood needles. Significant improvement in park visibility on both the clearest and haziest days have been documented since the late 1980’s Still, visibility needs improvement to reach the Clean Air Act goal of no human caused impairment.

Visibility effects:

  • Reduction of the average natural visual range from about 110 miles (without the effects of pollution) to about 90 miles because of pollution at the park
  • Reduction of visual range to below 45 miles on high pollution days

Visit the NPS air quality conditions and trends website for park-specific visibility information. Redwood NSP has been monitoring visibility since 1988. Explore air monitoring »

Ground-Level Ozone

Red alder leaves
Red Alder is one of the ozone-sensitive species found at Redwood NSP.

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.

Over the course of a growing season, ozone 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. An ozone monitor from 1987–1995 at Redwood NSP reported low ozone concentrations compared to other California parks (Sullivan et al. 2001). A risk assessment that concluded that plants in Redwood NSP were at moderate risk of ozone injury on plant leaves (Kohut 2007; Kohut 2004). The U.S. Forest Service did not find ozone injury on trees examined near the park (specifically, in the northern end of the North Coast air basin) (Campbell et al. 2007). However, that survey did not look at understory plants. Some plants are more sensitive to ozone than others. Ozone-sensitive plants in Redwood NSP include Pinus jeffreyi (Jeffrey pine), Alnus rubra (red alder), and Artemisia douglasiana (Sagebrush). Search for more ozone-sensitive plant species found at Redwood NSP.

Campbell, S. J., Wanek, R. Coulston, J. W. 2007. Ozone injury in west coast forests: 6 years of monitoring. General Technical Report. PNW-GTR-722. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 53 p. Available at https://www.fs.usda.gov/pnw-beta/publications/ozone-injury-west-coast-forests-6-years-monitoring.

Clark, C.M., Simkin, S.M., Allen, E.B. et al. Potential vulnerability of 348 herbaceous species to atmospheric deposition of nitrogen and sulfur in the United States. Nat. Plants 5, 697–705 (2019). https://doi.org/10.1038/s41477-019-0442-8

Geiser, Linda & Nelson, Peter & Jovan, Sarah & Root, Heather & Clark, Christopher. (2019). Assessing Ecological Risks from Atmospheric Deposition of Nitrogen and Sulfur to US Forests Using Epiphytic Macrolichens. Diversity. 11. 87. 10.3390/d11060087.

Geiser, Linda & Root, Heather & Smith, Robert & Jovan, Sarah & Clair, Larry & Dillman, Karen. (2021). Lichen-based critical loads for deposition of nitrogen and sulfur in US forests. Environmental Pollution. 291. 118187. 10.1016/j.envpol.2021.118187.

Horn KJ, Thomas RQ, Clark CM, Pardo LH, Fenn ME, Lawrence GB, et al. (2018) Growth and survival relationships of 71 tree species with nitrogen and sulfur deposition across the conterminous U.S.. PLoS ONE 13(10): e0205296. https://doi.org/10.1371/journal.pone.0205296

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.

Kohut RJ. 2004. Northern Colorado Plateau Network Ozone Risk Assessment. National Park Service. Fort Collins, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2181489.

McCoy K., M. D. Bell, and E. Felker-Quinn. 2021. Risk to epiphytic lichen communities in NPS units from atmospheric nitrogen and sulfur pollution: Changes in critical load exceedances from 2001‒2016. Natural Resource Report NPS/NRSS/ARD/NRR—2021/2299. National Park Service, Fort Collins, Colorado. https://doi.org/10.36967/nrr-2287254.

[NADP] National Atmospheric Deposition Program. 2018. NTN Data. Accessed January 20, 2022. Available at http://nadp.slh.wisc.edu/NADP/

Porter, E., Blett, T., Potter, D.U., Huber, C. 2005. Protecting resources on federal lands: Implications of critical loads for atmospheric deposition of nitrogen and sulfur. BioScience 55(7): 603–612. https://doi.org/10.1641/0006-3568(2005)055[0603:PROFLI]2.0.CO;2

Sullivan T.J., Peterson, D.L., Blanchard, C.L., Tannebaum, S.J. 2001. Assessment of Air Quality and Air Pollutant Impacts in Class I National Parks of California. National Park Service. Available at https://irma.nps.gov/DataStore/Reference/Profile/2082158.

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, CO.

Part of a series of articles titled Park Air Profiles.

Redwood National and State Parks

Last updated: December 5, 2022