Kevin Wilson, a senior scientist in Berkeley Lab’s Chemical Sciences Division, is the 2024 winner of the David A. Shirley Award for Outstanding Scientific Achievement at the Advanced Light Source (ALS). His selection, by members of the ALS Users’ Executive Committee (UEC), recognizes Wilson’s development of innovative vacuum ultraviolet (VUV) and x-ray aerosol measurement techniques for the study of chemical interactions at the gas–aerosol interface.
What is the focus of the work you’re being recognized for?
My group is primarily focused on aerosols in an urban setting. This includes anthropogenic emissions from combustion, but aerosols also form spontaneously in the atmosphere due to oxidation of trace gases. And here in the Bay Area there are also marine aerosols that we see basically every day when the fog rolls in. Each of those aerosols has a distinct chemical composition and set of chemistries that we want to understand.
Our use of vacuum ultraviolet (VUV) aerosol mass spectrometry to look in detail at chemical reaction mechanisms at the air–particle interface is where I would say our work has had the biggest impact. We use VUV photoionization mass spectroscopy at Beamline 9.0.2 to give us very clean mass spectra of complex organic systems. For instance, we can see how an organic aerosol, like diesel exhaust, ages in the atmosphere. A synchrotron is a very bright and tunable source of VUV. You can tune the beam to different ionization energies to distinguish, for example, polyaromatic hydrocarbons from alkanes and things like that. It’s a tool that allows us to follow chemical reactions in aerosol particles with molecular specificity.
We also use soft x-rays at Beamline 9.0.1 to complement our VUV work. The x-rays give us surface-specific information on the aerosols and functional group information. If we also understand the chemistry happening on a single aerosol system using VUV, we should be able to reconcile both of those measurements to get a more complete picture.
What early experiences inspired you to become a scientist?
I actually ended up falling into science in college at Willamette University. I’d planned to major in political science, but I had to take a general education science course in college and decided to take chemistry. All of my friends told me it was a mistake because it was a really hard class. But it was taught by a phenomenal teacher, Frances Chapple, and it was an incredibly exciting class in large part because of the way she taught it. I got hooked, and later I took a physical chemistry class. This is a very geeky thing to say, but we did a measurement and assignment of the rovibrational spectrum of HCl in the gas phase, and it was amazing. The spectrum is beautiful, and it captivated me. Before I knew it, I ended up with a chemistry degree.
How did you move into synchrotron work from there?
It didn’t happen right away. I ended up going to Los Alamos as a student intern and worked in a physical chemistry lab there on polar stratospheric cloud chemistry. At night I would drive down to Santa Fe and take night classes in the humanities at St. John’s, and I actually ended up getting a master’s in humanities. So I had this dual life, and at some point you have to decide what you want to do with your career, and so I ended up applying to graduate school in chemistry and came to work for Rich Saykally at UC Berkeley.
He was starting this project on using x-rays to look at liquid jets. He teamed up with Jim Tobin, who was a synchrotron person here at the ALS. And so we ended up building an endstation with lots of help, in particular from Bruce Rude and Tony Catalano. I actually had an ALS Doctoral Fellowship that supported me, and I spent most of my PhD at the ALS. For my thesis work, I built up a couple versions of a liquid jet endstation to do x-ray absorption. We were mainly looking at liquid water aqueous solutions, so the solvation structure around ions and the structure of liquids as probed by x-rays—very basic things like water, methanol, and water–methanol solutions.
I moved back to Los Alamos to do a postdoc after my PhD, and I did non-synchrotron aerosol work. After a while, my wife and I were looking back to the Bay Area for a variety of reasons. I started talking to Musa Ahmed, who I knew in passing when I was a graduate student, and Steve Leone, who was the director of the Chemical Dynamics Beamline. They were interested in starting some aerosol work, and so I moved back to work at Berkeley Lab.
What’s an example of some recent impactful work you’ve done?
An example I’m pretty excited about is work we published a few years ago in PNAS that pointed to a new connection between peroxy radicals and Criegee intermediates. Peroxy radicals are thought of as being very important in hydroxyl radical reactions, and Criegee intermediates are thought of as the key intermediate that governs reactions with ozone. It was long assumed that these two reaction pathways are very distinct—that there’s not a lot of crossover between these two oxidation mechanisms. Working with a postdoc of mine, Meirong Zeng, we found that there are connections between peroxy radicals that can directly form Criegee intermediates. These connections are important to understand oxidation in the atmosphere but also for example, in living cells. And in fact, this is a potential additional mechanism to explain auto oxidation, which is how organics, including food, degrade in the environment.
What advice do you have for scientists starting out in their careers?
I would say to trust yourself about what a good science question is. I think there’s a tendency to be swept up and follow the crowd sometimes. A lot of what I do is at the boundary between basic chemistry and atmospheric chemistry. Early on in my career, it felt uncomfortable sometimes that I wasn’t doing the kind of atmospheric chemistry that the rest of the field was doing, but over time I feel like the atmospheric community has come to really appreciate the work. I encourage my students and postdocs to develop that intuition to develop your own scientific questions and trust that they’re good ones rather than just following what happens to be trendy.
The Shirley Award is named after David Shirley, a professor of chemistry at UC Berkeley and director of Berkeley Lab from 1980 to 1989, whose vision was instrumental in building the ALS. Recipients of the award are selected by members of the ALS UEC, with input from ALS staff members representing the Recognition Task Force of the ALS Inclusion, Diversity, Equity, & Accountability (IDEA) Committee.