Johnston, Harold S. (1920- )

American geochemist

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 Earth's ozone layer. Johnston's 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 1948. That same year he married Mary Ella Stay, and the couple eventually had four children. Johnston was on the faculty of the chemistry department at Stanford University from 1947 to 1956 and the California Institute of Technology from 1956 to 1957. He then became a professor of chemistry at the University of California, Berkeley, serving as dean of the College of Chemistry from 1966 to 1970.

Johnston's introduction to meteorology occurred when he was a civilian scientist working on a defense project in World War II. In 1941, Roscoe Dickinson, Johnston's research director at the California Institute of Technology, was over-seeing a National Defense Research Council project, with which Johnston became involved. Dickinson's group tested the effects of poisonous volatile chemicals on charcoals that were to be used in gas masks. Later, they studied how gas clouds moved and dispersed under different conditions in order to appraise coastal areas that might be vulnerable to chemical attacks.

In 1943, Johnston moved with the Chemical Warfare Service to Bushnell, Florida, where he worked with, and eventually headed, the Dugway Proving Ground Mobile Field Unit of the U.S. Chemical Warfare Service. This unit carried out test explosions to assess how the dispersion of gas was affected by meterological changes. While he was there, Johnston and John Otvos developed an instrument to measure the concentration of various gases in the air.

Johnston applied his meteorology work to his Ph.D. studies, which he resumed in 1945. He wrote his thesis on the reaction between ozone , a naturally occurring form of oxygen , and nitrogen dioxide, a pollutant formed during combustion. Later, during his tenure at Stanford, Johnston worked on a series of fast gas-phase chemical reactions. Using photo-electron multiplier tubes left over from the war, he pioneered a method of studying gas phase reactions that was a thousand times faster than existing techniques. Johnston then spent the years 1950 to 1956 researching high and low pressure limits of unimolecular reactions, and for the subsequent ten years, expanded his research to apply activated complex theory to elementary bimolecular reactions.

One of Johnston's most significant research efforts has been on the destruction of the ozone layer. This layer in the earth's upper atmosphere protects people from the Sun's ultra-violet rays . Chlorofluorocarbons (CFCs)—gaseous compounds often used in aerosol cans, refrigerants, and air conditioning systems—deplete this ozone layer, resulting in increased amounts of harmful radiation reaching the earth's surface. The Environmental Protection Agency has imposed production cutbacks on these harmful chemicals. Much like CFCs, nitrogen oxides also damage the ozone layer. During the late 1960s, the federal government financed the design and construction of two prototype supersonic transport (SST) aircraft. An intense political debate over whether the program should be expanded to construct five hundred SSTs was waged. Although Congress was split almost evenly, both houses voted to terminate the SST program in March, 1971. Johnston's articles and testimony suggesting the negative effects SSTs could produce on the atmosphere led two senators to introduce the Stratosphere Protection Act of 1971, which established a research program concerned with the stratosphere. The resulting 1971 program, with which Johnston was affiliated, was called the Climatic Impact Assessment Program (CIAP). Among other things, CIAP concluded that nitrogen oxides from stratospheric aircraft would further reduce ozone. CIAP recommended that aircraft engines be redesigned to reduced nitrogen oxide emissions.

Throughout his career, Johnston has served on many state and federal scientific advisory committees. In the 1960s, he was a panel member of the President's Science Advisory Board on Atmospheric Sciences and was on the National Academy of Sciences (NAS) Panel to the National Bureau of Standards. Johnston served on the California Statewide Air Pollution Research Center committee and the NAS Committee on Motor Vehicle Emissions during the early 1970s. He also served on the Federal Aviation Administration's High Altitude Pollution Program from 1978 to 1982 and the NAS Committee on Atmospheric Chemistry from 1989 to 1992. He has been an advisor to High Speed Civil Transport Studies for the National Aeronautics and Space Administration (NASA) since 1988.

Johnston is the author of the book Gas Phase Reaction Rate Theory and the author or coauthor of more than 160 technical articles. He is a member of the NAS, the American Academy of Arts and Sciences, the American Chemical Society, the American Physical Society, the American Geophysical Union, and the American Association for the Advancement of Science. Among Johnston's numerous awards are the 1983 Tyler Prize for Environmental Achievement, the 1993 NAS Award for Chemistry in Service to Society, and an honorary doctor of science degree from Emory University.

See also Global warming; Greenhouse gases and greenhouse effect; Ozone layer and hole dynamics; Ozone layer depletion