Citation for Alexander Turner

Alexander Turner, winner of the 2020 James R. Holton Award
Alexander Turner

Alexander Turner receives the James R. Holton Award for his groundbreaking contributions to atmospheric sciences, including advances in atmospheric chemistry, climate, and the carbon cycle.

Atmospheric methane has proven a challenge to interpret, and definitive answers to why methane has gone through periods of growth, stabilization, and growth in the past 30 years have proven elusive. Historically, the primary atmospheric loss mechanism, the hydroxyl radical (OH), has been treated as effectively constant in time (supported by inferred stability in OH from methyl chloroform observations), and thus changes in atmospheric growth have been linked and attributed to changes in sources. Alex demonstrated that OH levels could have shifted in conjunction with changes in atmospheric methane while still being consistent with methyl chloroform observations. This changes the perspectives of recent atmospheric variability, as it elegantly illustrates that subtle changes in OH could explain some changes in atmospheric methane and that variable OH must be considered as we move forward.

While Alex has built on this work in expected directions (continuing analysis of recent changes in methane), he has also demonstrated powerful lateral thinking that has led to significant insights. He has considered how OH may vary on different timescales and in correlation with different climate/weather features. This culminated in a model study covering a 6,000-year period linking variability in OH to the El Niño–Southern Oscillation (ENSO). This work linked climate and chemistry in a manner not previously considered and has implications for how we consider and interpret contemporary methane.

Alex’s body of work is extensive, and beyond methane he has made contributions to mathematical methods for inverse modeling as well as developing new approaches combining multiple data streams to infer photosynthesis from space-based observations.

It is a pleasure to present the James R. Holton Award to Dr. Alexander Turner.

—Eric Kort, University of Michigan, Ann Arbor


I am deeply honored to receive this award. Speaking frankly, I was shocked when I received an email about it from AGU. It would have been flattering to know that I was nominated, let alone to receive this award. I never had the honor of meeting Jim Holton, but his impact on the field is obvious to all. I distinctly remember getting a copy of his textbook as a first-year graduate student; it felt like the first step toward becoming an atmospheric scientist. Receiving an award bearing his name is flattering, truly.

This award is particularly special to me because among the many prominent past recipients, my former undergraduate research adviser, Arlene Fiore, was the second to receive it. She is someone whom I deeply admire and one of the people who inspired me to pursue a career in atmospheric science. Being included on a short list with so many luminaries in the field is simply humbling.

There is a long list of brilliant and passionate scientists who have influenced me along the way. A few who stand out are Daven Henze for introducing me to research—I would not be an atmospheric scientist had I not met him as an undergraduate; Daniel Jacob for his unwavering support as I stumbled and grew through my dissertation; Ron Cohen for the freedom to explore an eclectic set of topics and invaluable feedback; and Inez Fung for continually pushing me to ask interesting questions. As I prepare to start my career, I hope I can emulate a fraction of those great scientists I learned from and support young scientists as they pursue their studies in atmospheric science.

—Alexander Turner, University of Washington, Seattle

Citation for Megan D. Willis

Megan Willis, winner of the 2020 James R. Holton Award
Megan D. Willis

Megan Willis receives the James R. Holton Award for her groundbreaking contributions to atmospheric science, in particular, the importance of aerosol composition in remote and polluted environments.

Megan’s doctoral research made extensive use of an aerosol mass spectrometer, and early in her degree she led experiments in which a new version of the instrument, which included the ability to measure soot-containing particles, was characterized. Using measurements collected from a roadside site, Megan was able to quantify the mixing state of black carbon (soot) from traffic, with important implications for air quality and climate. She also collaborated on a number of studies in which the instrument was used in a laboratory, to probe the impacts of oxidation on soot particles, and in the field, to characterize carbonaceous particles in an industrially influenced boreal region.

Megan’s most significant contributions were made during her participation in NETCARE (Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments). Megan published two first-author articles demonstrating the importance of biogenic compounds for the growth of small particles in the Arctic atmosphere during the summer. Those studies reported the first observations of the growth of newly formed particles in the Arctic marine environment and identified secondary chemistry as a likely contributor. Her work provides new information about how local ocean–atmosphere feedbacks via atmospheric chemistry and aerosol–cloud interactions may change as the Arctic climate system warms. A subsequent paper focused on disentangling the many factors contributing to aerosol loading during springtime in the Arctic—when the impact of lower latitudes on the region is more significant. Given her extensive work in this area, Megan is now one of the community’s experts on the processes affecting Arctic aerosol composition, and she published a review article on the subject in 2018.

—Jennifer Murphy, University of Toronto, Toronto, Ont., Canada


I’d like to begin by expressing my gratitude to the AGU Atmospheric Sciences section for this award. It is both humbling and inspiring to receive an award bearing John Holton’s name, and I aspire to live up to his legacy as a scientist, mentor, teacher, and community member. I’m also humbled to receive this award alongside Alex Turner, whose work I admire.

I am fortunate to be supported by an incredible community of scientists and mentors. I’ve had the opportunity to both learn from and work with many kind, smart, and passionate people around the world in my short career. Our field is becoming increasingly interdisciplinary, and so I can’t imagine working without the collaboration and generosity inherent to this community.

While many people have supported and guided me along the way, I’d like to express my gratitude to a few people explicitly: Erik Krogh and Chris Gill for igniting my enthusiasm for environmental chemistry; my Ph.D. adviser, Jon Abbatt, for opening my awareness to a wide world of questions in atmospheric chemistry, for his tireless support, and for always gently pushing me farther than I thought I could go; and Kevin Wilson for giving me the opportunity to think about atmospheric chemistry from a different perspective and for putting up with me, a fieldwork person, while I tried to learn laboratory physical chemistry.

Finally, I am deeply grateful to Kevin Worthington and the rest of my family for their unconditional support. I would be nowhere without them.

—Megan Willis, Colorado State University, Fort Collins


(2021), Turner and Willis receive 2020 James R. Holton Award, Eos, 102, Published on 06 July 2021.

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