Harold S. Johnston has been recognized as one of the world's leading authorities in atmospheric chemistry. He was among the first to suggest that nitrogen oxides might damage the Earth's ozone layer. His research interests have been in the field of gas-phase chemical kinetics and photochemistry, and his expertise has been employed by many state and federal scientific advisory committees on air pollution, motor vehicle emissions, and stratospheric pollution.

Harold Sledge Johnston was born on October 11, 1920, in Woodstock, Georgia, to Smith L. and Florine Dial Johnston. He graduated with a chemistry degree from Emory University in 1941 and, later that year, entered the California Institute of Technology as a graduate student. During the early 1940s, he was a civilian meteorologist attached to a United States Army unit in California and Florida, after which time he returned to graduate studies and earned his Ph.D. in chemistry and physics in...