About the editors Allan H. Legge is Professional Associate at The Kananaskis Centre for Environmental Research at The University of Calgary, Alberta, in Canada. He is a member of the TE--2 Ecological Effects Committee of the Air Pollution Control Association, the Canadian Petroleum Association Environmental Research Advisory Council, and a number of other associations. Dr. Legge received his PhD in plant genetics in 1971 from Oregon State University, Corvallis, and has been active in air pollution research on forest ecosystems since 1973. He was principal investigator of the ten--year multidisciplinary West White--court Case Study which investigated the long--term effects of sulphur gas emissions on the boreal forest in western Canada. Dr. Legge is currently principal investigator of biophysical aspects of the seven year Alberta Government--Industry/Acid Deposition Research Program which started in February 1985. Sagar V. Krupa is a Professor in the Department of Plant Pathology at the University of Minnesota in St. Paul. He is a member and past chairman of the TE--2 Ecological Effects Committee of the Air Pollution Control Association, and is at present a member of its Technical Council. He received his PhD from the Natural Sciences and Mathematics Faculty of the University of Uppsala, Sweden. Dr. Krupa has been conducting research and teaching in the field of air pollution since 1972.