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	USDA Forest Service 1400 Independence Avenue SW Washington, D.C. 20250-0003 (202) 205-8333

Wilderness Air Quality Monitoring

An air quality samplers being setup for monitoring

An example of air quality samplers being setup for monitoring.

Forest Service managers directly monitor and use models to measure or estimate the amount of acid deposition occurring on the national forests and how this deposition is affecting Forest resources. Long-term air quality and resource monitoring on and near the National Forests and Class I areas has helped establish air pollution trends and existing condition of the resources. Based on these existing conditions, and documented cause and effect relationships, the air resource specialists in the Forest Service are identifying critical loads and resource concern thresholds for evaluating potential impacts of new sources of air pollution for each Class I Area.

Critical and Target Loads

Forest Service air resource specialists are also working to establish critical and target loads for Class I areas to help evaluate adverse effects from air pollution. A critical load can be defined as "a quantitative estimate of the exposure to one or more pollutants below which significant harmful effects on specific sensitive elements of the environment do not occur according to present knowledge". A target load is set based on policy and management direction, and depending on whether or not current critical loads values have been exceeded, a target load can be above or below the critical load. In general, the critical load is based on modeled or measured dose-response data, while target load can be based on political, economic, spatial, or temporal considerations in addition to scientific information.

Why Develop Critical and Target Loads?

Defining the critical and target loads for areas on the Forest helps resource managers communicate the effects of air pollution on sensitive resources to Forest Service decision-makers as well as to air regulators. This information will also be used to assess how some management activities may exacerbate air pollution related problems or identify areas where mitigation may be an option for resources that have already been negatively affected. This information can be used in a regulatory context when consulting with and advising air regulatory agencies on effects to Forest resources resulting from new and existing sources of air pollution. For more information on critical loads and the related science, please visit the Forest Service Northern Research Station, the EPAs website for Acid Rain or download the USFS Ecological Effects.