Karl Gast has spent a large portion of his career measuring atmospheric trace gas concentrations. He received a Master of Science degree from the University of Denver in 1986 after studying the infrared absorption and emission by atmospheric trace gases using long path interferometers, grating spectrometers, and a laser heterodyne spectrometer. In 1997, Karl received his Doctor of Philosophy degree from the University of Arizona by developing a new technique for measuring tropospheric concentrations of hydroxyl radicals. He has employed a wide variety of optical and chemical measurement techniques in pursuing his research interests and has been fortunate to associate with several outstanding scientists. Karl currently works in Tucson developing, updating, and maintaining optical sensor designs.