APA

Walsh, N., Carlson, C., & States. Forest Service. Northern Region. State & Private Forestry, U. (1978). The effect of low-level sulfur dioxide on sensitive vegetation : a background document for use in assessing air quality redesignation for primitive areas as required by the Clean Air Act Amendments of 1977 (P.L. 95-95). : Missoula, MT. : Forest Insect & Disease Management, USDA, Forest Service, Northern Region, State & Private Forestry.