Professor Marcel Nicolet has been awarded the William Bowie Medal for 1984 because of his contribution to the elucidation of the chemistry of the earth's upper atmosphere and for acting as Secretary General of the Special Committee of the International Geophysical Year (1953–1960). Marcel Nicolet has made a greater contribution to our understanding of the chemistry of the earth's upper atmosphere than any other single individual alive or dead. Some of the contributions are (1) determination of photoionization and photodissociation coefficients; (2) showed the importance of diffusion in determining concentration profiles in the thermosphere; (3) elucidated the mechanism for the infrared airglow formation; (4) predicted the presence of the He layer; (5) explained the formation of the D region as due to NO ionization by Lyman-α radiation and cosmic rays; (6) predicted the presence of NO, NO2, HNO3, HO2, and H2O2 in the upper atmosphere before they were measured; (7) was the first to recognize the importance of NOx (NO, NO2), and HOx (HO, HO2) in the upper atmosphere; (8) was the first to conclude that N2O by its reaction with O(1D) is important in the stratosphere as a source of NO.