Johnston was born in Woodstock, Georgia. His father, Smith Lemon Johnston, helped to run his family's general store. They lived on a Georgia farm when Harold Johnston was young. In the early 1930s, Johnston contracted rheumatic fever and the illness affected his heart. A physician uncle told Johnston's father not to send Johnston to college because the young man would not survive long enough to get much use out of the education. Johnston said he later learned that the disease was associated with an average survival period of fifteen years at the time. Going to college at Emory University with aspirations of becoming a journalist, Johnston soon realized that the U.S. was headed toward World War II and that a science degree would serve him better. Johnston completed an undergraduate degree in chemistry and a minor in English literature. Johnston received a Ph.D. in chemistry and physics from the California Institute of Technology. As a doctoral student, Johnston focused on the interaction of ozone and the pollutant nitrogen dioxide. While at Caltech, he joined in a secret defense project that involved protecting the country against the use of gas warfare.
Career
From 1947 to 1956, Johnston taught at Stanford University. While there, he was named to the editorial board of the Journal of the American Chemical Society. In the early 1950s, Johnston furthered the air pollution work of Arie Jan Haagen-Smit by showing that free-radical reactions underlay the photochemical process leading to smog. Throughout his career, much of Johnston's work involved understanding the kinetics of nitrogen oxides. He returned to Caltech as a faculty member for a year in 1956. From 1957 until his retirement in 1991, Johnston was a professor at the University of California, Berkeley. From 1966 to 1970, Johnston was the dean of Berkeley's College of Chemistry. Johnston mentored undergraduate and graduate students, including future Nobel Prize winner Dudley R. Herschbach and future National Medal of Science winner Susan Solomon. He also made large contributions to the theory of elementary chemical reactions. He wrote a popular textbook on reaction rate theory. Johnston became best known for his work related to ozone. In a 1971 paper, he posited that pollution from supersonic aircraft in the stratosphere could deplete the ozone layer. Because it suggested for the first time that human activity could impact the integrity of the environment, Johnston's ozone research received some criticism and resistance. However, two environmental regulatory programs were formed as a result of his findings – the Climatic Impact Assessment Program and the Stratosphere Protection Program. At Johnston's retirement party when he stepped down as dean of the College of Chemistry, he told me this story, part of which was told to him by a former student who was working in Washington. After he published his paper about supersonic aircraft and the ozone layer, President Richard Nixon called in his science advisor. Nixon did not ask whether Johnson was correct. He asked, "How can we discredit this guy?" The science advisor recalled that a government agency had recently published a book on gas phase kinetics. He said he would find out who the author was and ask him to refute Johnston. It turned out that Johnston was the author. So, Nixon gave up, and the fleet of SSTs was never built. I have no source for this story other than what Dean Johnston told me. I was a Ph.D. candidate at the time.
Even in the late 1990s, Johnston said that he had lived most of his life with "a moving 10-year life expectancy" because of his early bout with rheumatic fever, but he remained in good health until he was more than 90 years old. He died in 2012; he was 92. Johnston was survived by his wife of 64 years, Mary Ella, and their four children, as well as several grandchildren and great-grandchildren.
