USDA Forest Service

Pacific Southwest Research Station

Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Research Topics Air Quality

Trees in the foreground with photochemical smog hindering the visability of the mountains and San Joaquin Valley in the distance.
From Sequoia National Park, photochemical smog is visible over the San Joaquin Valley. (National Park Service)

Air pollution affects climate change and has important effects on the health of forests and people.

Many common air pollutants and greenhouse gases, such as carbon dioxide (CO2), methane (CH4), and atmospheric aerosols (including black carbon, soot), have common sources, and interact in the atmosphere, causing a variety of environmental impacts at local, regional and global scales.

The combined effects of numerous climate change and air pollution factors may significantly differ from the sum of separate effects due to various interactions of the elements.

The air pollutants that have the greatest effect on forest growth and health are tropospheric ozone (O3) and reactive nitrogen compounds, such as nitrogen oxides (NOx), ammonia (NH3), nitric acid vapor (HNO3), and aerosol ammonium (NH4+) and nitrate (NO3-).

Pacific Southwest Research Station (PSW) scientists focus their research on O3 and nitrogen (N) deposition because these air pollutants have been found to have the most pronounced effects, both directly and indirectly, on U.S. forests and other terrestrial ecosystems. To gauge the effects of air pollution on the health of residents and visitors on forested federal lands, researchers are studying the impacts of O3 and particulate matter (PM2.5 and PM10), two pollutants controlled by federal and California ambient air quality standards.

Southern California and California's Central Valley are among the most air pollution-affected areas in North America. Ozone, nitrogenous gases and aerosols are transported long distances to forests in the Sierra Nevada and the Transverse Ranges of southern California. Although emission control devices required in the state of California on both industrial and mobile sources have significantly reduced the number of days that exceed state and federal O3 ambient air quality standards, the overall pollutant exposures are still very high and potentially harmful. Therefore, our goal is to provide scientific knowledge that may help in setting protective air quality standards and to evaluate the effects of pollution exposure on forests and other ecosystems.

Although our research is focused on the issues most important to California and the western U.S., PSW has also developed extensive collaborations with scientists and managers at the state, regional, national and international scales. We collaborate with partners such as the National Park Service, U.S. Environmental Protection Agency, U.S. Geological Survey as well as various universities and research institutes in North America, Europe and Asia. We also actively participate in the International Union of Forest Research Organizations (IUFRO), specifically the Research Group 7.01 "Impacts of Air Pollution and Climate Change on Forest Ecosystems" and the IUFRO Task Force "Climate Change and Forest Health."

Major Research Initiatives

Major Research Initiatives

Emerging Research

Emerging Research

More information
  • Fenn, M.E.; Allen, E.B.; Geiser, L.H.; 2011. Mediterranean California. In: Pardo, L.H.; Robin-Abbott, M.J.; Driscoll, C.T., eds. Assessment of nitrogen deposition effects and empirical critical loads of nitrogen for ecoregions of the United States. Gen. Tech. Rep. NRS-80. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 143-169.
  • Fenn, M.E.; Lambert, K.F.; Blett, T.F.; Burns, D.A.; Pardo, L.H.; Lovett, G.M.; Haeuber, R.A.; Evers, D.C.; Driscoll, C.T.; Jeffries, D.S. 2011. Setting limits: using air pollution thresholds to protect and restore U.S. ecosystems. Issues in Ecology, Report Number 14. J.S. Baron, Editor-in-Chief. Ecological Society of America. Washington, D.C.
  • Pardo, L.H.; Fenn, M.E.; Goodale, C.L.; Geiser, L.H., et al. 2011. Effects of nitrogen deposition and empirical nitrogen critical loads for ecoregions of the United States. Ecological Applications. 21(8): 3049-3082.
  • Bytnerowicz, A.; Fenn, M.; Long, J.W. 2014. Air quality. In: Long, J.W., Quinn-Davidson, L., Skinner, C.N., eds. Science synthesis to support socioecological resilience in the Sierra Nevada and southern Cascade Range. Gen. Tech. Rep. PSW-GTR-247. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 471-495. Chap. 8.1.
  • Bytnerowicz, A.; Fenn, M.; Allen, E.B.; Cisneros, R. 2016. Atmospheric Chemistry. In: Mooney, H.; Zavaleta E., eds. Ecosystems of California. University of California Press. Oakland, California: 107-128.
Last Modified: Nov 30, 2018 11:42:50 AM