Air quality at Joshua Tree National Park
Most visitors who come to national parks expect clean air and clear views. However, Joshua Tree National Park (NP), California, home to the famously twisted, spiky Joshua tree, is significantly affected by air pollution. Most of this pollution is generated in California’s Los Angeles basin and moves inland with the predominant westerly winds. Air pollutants blown into the park can harm natural and scenic resources such as soils, surface waters, plants, and visibility. The National Park Service works to address air pollution effects at Joshua Tree NP, and in parks across the U.S., through science, policy and planning, and by doing our part.
Nitrogen and sulfur
Nitrogen and sulfur compounds deposited from the air may have harmful effects, including nutrient imbalances and loss of biodiversity. Arid ecosystems found in Joshua Tree NP are particularly vulnerable to excess nitrogen which can lead to nutrient enrichment, a processes that changes soil chemistry and alters plant communities. Research in the park has found elevated soil nitrogen levels that are responsible for increased growth of invasive nitrogen-loving grasses. These grasses out-compete native plant species, leading to native plant species decline and reduced biodiversity. Additionally, the spread of weedy grasses that burn quickly increases fire risk (Allen et al. 2009; Rao et al. 2010).
Healthy ecosystems can naturally buffer a certain amount of pollution, but as nitrogen and sulfur accumulate, a threshold is passed where the ecosystem is harmed. “Critical load” is a term used to describe the amount of pollution above which harmful changes in sensitive ecosystems occur (Porter 2005). Nitrogen deposition exceeds the critical load for one or more park ecosystems (NPS ARD 2018).
Visit the NPS air quality conditions and trends website for park-specific nitrogen and sulfur deposition information. Joshua Tree NP has been monitoring nitrogen and sulfur deposition since 2000. Explore air monitoring »
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. Joshua Tree NP experiences high ozone concentrations, with peak levels and cumulative doses that are some of the highest in the NPS.
Especially 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, Joshua Tree NP staff post health advisories cautioning visitors of the potential health risks associated with exposures to elevated levels.
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. While the generally dry conditions in the park are likely to limit ozone uptake by plants, a wet year or strong summer monsoon season may increase the risk of ozone injury. There are a few ozone-sensitive plants in the park including Salix gooddingii (Goodding’s willow). Limited assessments in the park have not documented ozone injury to vegetation growing naturally in the field (Temple 1989); however, no assessment has been made of other ozone effects such as growth effects. A study of Rhus trilobata conducted in a park biomonitoring plot demonstrated that under irrigated conditions the plants showed typical ozone injury symptoms (Temple 1989), demonstrating that ozone levels are sufficiently high in Joshua Tree NP to damage plant leaves, and possibly reduced growth effects, under certain conditions (Sullivan et al. 2001). Search ozone-sensitive plant species found at Joshua Tree NP.
Visit the NPS air quality conditions and trends website for park-specific ozone information. Joshua Tree NP has been monitoring ozone since 1993. Check out the live ozone and meteorology data from Joshua Tree NP and explore air monitoring »
Many visitors come to Joshua Tree NP to enjoy the spectacular vistas, including that of the Mexican border from the mile-high vantage point of Keys View. Unfortunately, park 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, 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.Visibility effects:
- Reduced visibility on many days due to haze
- Reduction of the average natural visual range from about 160 miles (without the effects of pollution) to about 100 miles because of pollution at the park
- Reduction of the visual range from about 120 miles to below 55 miles on high pollution days
Visit the NPS air quality conditions and trends website for park-specific visibility information. Joshua Tree NP has been monitoring visibility since 2000. Check out the live air quality webcam and explore air monitoring »
Allen, E. B., Rao, L. E., Steers, R. J., Bytnerowicz, A., and Fenn, M. E. 2009. Impacts of atmospheric nitrogen deposition on vegetation and soils in Joshua Tree National Park. Pages 78–100 in R. H. Webb, L. F. Fenstermaker, J. S. Heaton, D. L. Hughson, E. V. McDonald, and D. M. Miller, eds. The Mojave Desert: Ecosystem Processes and Sustainability. University of Nevada Press, Las Vegas.
Bytnerowicz, A., Olszyk, D. M., Fox, C. A., Dawson, P. J., Kats, G., Morrison, C. L., and Wolf, J. 1988. Responses of desert annual plants to ozone and water stress in an in situ experiment. Journal of Air Pollution Control Association 38: 1145–1151.
Fenn, M. E., Haeuber, G. S., Tonnesen, J. S., Baron, J. S., Grossman-Clarke, S., Hope, D., Jaffe, D. A., Copeland, S., Geiser, L., Rueth, H. M., and Sickman, J. O. 2003. Nitrogen emissions, deposition and monitoring in the western United States. Bioscience 53: 391–403.
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
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
Rao L. E., Allen E. B., Meixner T. 2010. Risk-based determination of critical nitrogen deposition loads for fire spread in southern California deserts. Ecological Applications 20 (5): 1320–1335.
Sullivan, T. J., McDonnell, T. C., McPherson, G. T., Mackey, S. D., Moore, D. 2011a. Evaluation of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from atmospheric nitrogen deposition: main report. Natural Resource Report NPS/NRPC/ARD/NRR—2011/313. National Park Service, Denver, Colorado. Available at https://www.nps.gov/articles/nitrogen-risk-assessment.htm
Sullivan, T. J., McDonnell, T. C., McPherson, G. T., Mackey, S. D., Moore, D. 2011b. Evaluation of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from atmospheric nitrogen deposition: Mojave Desert Network (MOJN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/330. National Park Service, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2168700
Sullivan, T. J., McPherson, G. T., McDonnell, T. C., Mackey, S. D., Moore, D. 2011c. Evaluation of the sensitivity of inventory and monitoring national parks to acidification effects from atmospheric sulfur and nitrogen deposition: main report. Natural Resource Report NPS/NRPC/ARD/NRR—2011/349. National Park Service, Denver, Colorado. Available at https://www.nps.gov/articles/acidification-risk-assessment.htm
Sullivan, T. J., McPherson, G. T., McDonnell, T. C., Mackey, S. D., Moore, D. 2011d. Evaluation of the sensitivity of inventory and monitoring national parks to acidification effects from atmospheric sulfur and nitrogen deposition: Mojave Desert Network (MOJN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/360. National Park Service, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2170591
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, Colorado. Available at https://www.nps.gov/articles/aqrv-assessment.htm
Temple, P. J. 1989. Oxidant air pollution effects on plants of Joshua Tree National Monument. Environ. Pollut. 57: 35–47.