Douglas D. Davis passed away unexpectedly on 26 December 2016, taking from us an invaluable atmospheric chemist. He was renowned for his creativity, leadership, and dogged pursuits of environmental issues.
Doug excelled in kinetics studies, pioneered a paradigm for airborne sampling, developed new measurement techniques, and enabled understanding of atmosphere-cryosphere interactions. He was one of the earliest atmospheric chemists, and he helped shepherd this field into the full-fledged discipline that it is today.
Doug was born in Madrid, Neb., on 23 February 1940. His bachelor’s and Ph.D. degrees were from the University of Washington (1962) and the University of Florida (1966). Following a research fellowship at the National Bureau of Standards (NBS), Doug spent 7 years (1969–1976) on the faculty of the Chemistry Department at the University of Maryland, College Park. He then moved to the Georgia Institute of Technology (Georgia Tech), where he was instrumental in establishing the School of Earth and Atmospheric Sciences. He retired in 2004 but continued as an emeritus professor until his death.
Advancing Our Knowledge of the Atmosphere
Doug established the rates of stratospheric and tropospheric reactions in the 1970s. He enhanced the flash photolysis technique that he had worked on at NBS as a postdoc so that he could use it study atmospheric kinetics.
His body of work on hydroxyl radical (OH•) and oxygen atom reaction kinetics in the 1970s was instrumental in improving our understanding of stratospheric ozone layer depletion and the formation of ozone pollution in the troposphere. Of particular note are his studies on the OH• reaction with hydrocarbons, which quantified the initial step in tropospheric ozone formation.
Doug also pioneered atmospheric chemistry measurement techniques. His ability to make use of new technology led to the measurement of OH• in the atmosphere using laser-induced fluorescence. Indeed, he was the founding father of this technique, and he developed one of the earliest methods for OH• detection in his pursuit to quantify this central radical in tropospheric chemistry. These efforts to quantify OH• in the troposphere were only partially successful. They paved the way for success a decade later, but these measurements remain a challenge even today.
With colleagues, Doug developed the two-photon laser-induced fluorescence detection of nitric oxide (NO). This innovation dramatically improved sensitivity by exciting NO molecules with two lasers of different wavelengths so that the fluorescence emitted would be blueshifted relative to the two pumping wavelengths, effectively enhancing the signal to noise ratio.
Airborne Measurements of Atmospheric Composition
Doug pioneered the use of multi-instrumented aircraft to examine the atmosphere. He installed instruments on a small research aircraft to make the first airborne sampling of a power plant plume in 1973. His work on this project was highlighted on the cover of Science magazine, which garnered him the honor of Maryland’s Outstanding Young Scientist of 1974.
This early success led to the ambitious Global Atmospheric Measurements Experiment on Tropospheric Aerosols and Gases (GAMETAG) project in 1977–1978. Doug and his colleagues packed an aircraft with a large number of complementary instruments provided by multiple principal investigators to characterize the composition of the atmosphere over the remote Pacific, between 0.5 and 6 kilometers above Earth’s surface at latitudes between 70°N and 58°S.
GAMETAG was truly the forerunner of modern aircraft sampling endeavors in the troposphere and the stratosphere, and it set the paradigm of using multiple instruments to sample the same air mass to decipher the chemistry of the atmosphere. GAMETAG is still emulated by airborne field studies today, albeit with more advanced airborne payloads.
Tracking the Human Influence
Over the next 2 decades, Doug led the design of airborne field studies. He examined various atmospheric phenomena, especially in the pristine atmosphere. He was a driving force behind NASA’s Global Tropospheric Experiment (GTE), and his collaboration with Reginald Newell of the Massachusetts Institute of Technology led to the highly successful series of Pacific Exploratory Missions in the 1990s.
These campaigns documented clear signals of human activity in pristine areas, demonstrating the effectiveness of long-range transport and anthropogenic influences on ozone and oxidation cycles on a global scale.
During a campaign in 1991, Doug and Reg conspired to measure the composition of air pumped through the intense convection of Typhoon Mireille, despite instructions from their NASA sponsors to avoid this storm. True to Doug’s reputation for persistence, he continued to plan along with Reg and the science team to sample an “organized convective event,” which received no objection from sponsors and resulted in one of the most talked about flights in the history of the GTE project.
After the flight, Doug recognized the need to identify a compound to serve as an effective tracer of convected air. Building on his seminal work on the role of iodine in the troposphere, he proposed reanalyzing air samples taken during the flight for naturally occurring methyl iodide. This was the first time that methyl iodide had been used as a tracer for convection, which is now common practice.
Late in his career, Doug’s curiosity was rewarded by an unexpected finding that would consume his attention until his passing. He found that reactive nitrogen released from the Antarctic snowpack created a photochemical environment that bore no resemblance to the pristine environment that had been assumed previously. Although the release of nitrogen from sunlit snow had been recently observed in the Arctic, the effect was dramatically magnified in the Antarctic. Doug devoted himself to understanding the controlling factors and effects of the chemistry in this unique environment, which continues to be a stimulating area of investigation in atmosphere-cryosphere research.
A Great Teacher and Mentor
Doug’s scientific curiosity was accompanied by an energy and intensity of purpose that made him an effective leader, and he never missed an opportunity for gaining new insight. Doug brought the same energy and excitement to the classroom. Armed with plenty of stories from the field, he delivered lectures that brought life to the subject of atmospheric chemistry as he developed his own curriculum for a topic that was constantly evolving.
Doug was a consensus favorite among the graduate students, despite his reputation for being one of the hardest professors. His marathon exams were considered a rite of passage. He mentored a vast number of graduate students and postdoctoral fellows, connecting him to an astonishing number of active scientists and leaders in the field today.
Doug is survived by Christine, his wife of nearly a half century. He is also survived by his daughter, Nicole; her husband, Brett; and their two daughters, Megan and Elizabeth.
An accomplished master gardener, Doug transformed his hillside home into a landscape recognized by the Atlanta botanical community. He also explored the world with Christine, visiting all seven continents, and he worked with prison inmates as a volunteer and mentor.
—Jim Crawford (email: [email protected]) and Gao Chen, Science Directorate, NASA Langley Research Center, Hampton, Va.; and A. R. Ravishankara, Department of Chemistry, Colorado State University, Fort Collins