Director, Division of Environmental Health, World Health Organization since 1986. Regional Advisor, Western Pacific Regional Office, World Health Organization, Philippines, 1985-1986. World Health Organization Air Quality Management Advisor, PEPAS, Malaysia, 1983-1985.
World Health Organization Air Quality Management Advisor, Ministry of Health, Representative of Korea, 1977-1983. Assistant Professor, Institute for Environmental Rch, University of Dortmund, Germany, 1973-1977. Assistant Professor, Institute of Physical Chem, University of Heidelberg, Germany, 1969-1972.