Using Spectroscopy to Explore the Chemistry and Impact of Environmental Interfaces

Thought LeadersVicki GrassianDistinguished Professor in the Department of Chemistry & BiochemistryThe University of California, San Diego

In this interview conducted at Pittcon 2024 in San Diego, we spoke to Professor Vicki Grassian, this year's recipient of the Pittsburgh Spectroscopy Award, about how spectroscopy serves as a crucial tool in uncovering the chemistry and impacts of environmental interfaces.

Could you please introduce yourself and give us an overview of your professional background? 

My name is Vicki Grassian, and I am currently a distinguished professor at the University of California, San Diego. I started my career at Albany University, where I received my bachelor’s degree and then my master’s degree at Rensselaer Polytechnic Institute before going to UC Berkeley for my Ph.D. 

What initially sparked your interest in the chemistry and impacts of environmental interfaces, and how has this passion evolved over your distinguished career?

My research in this area evolved over time. When I began my academic career, my research focused on surfaces that were important in heterogeneous catalysis. I then realized I could apply my background in surface chemistry to understanding complex environmental interfaces, i.e., their chemistry and impacts. I then started this new research area around the time I became an associate professor. It was then that I began to develop a strong interest in the environment, striving to understand broadly how interfaces play a role in the chemistry of the environment. 

Could you explain how the chemistry of environmental interfaces impacts our everyday lives and why it’s crucial for the general public to understand this field?

First of all, there is a wide range of environmental interfaces, such as particulate matter in the air and the surfaces of those particles, as well as minerals in groundwater and the interface between those solid minerals and the water system above it that may contain contaminants. These interfaces significantly impact air quality and water quality. They can even affect the climate because particles can nucleate clouds. Particles in the stratosphere can also play a role in the ozone layer. Environmental interfaces have critical impacts on health—including human health, ecosystem health, and planetary health. 

I think people are not aware of environmental interfaces. For example, here in San Diego, you can look out at the Pacific Ocean, which has an air-water interface. While polluted waters prompt warnings against swimming, there are less obvious processes occurring, like the exchange between the water and the air. We’re becoming more aware of these interactions in San Diego, particularly as we confront issues with sewer runoff and contamination into the Pacific Ocean. This awareness is leading to a growing demand for improvements to ensure both the quality of the air we breathe and the water we use.

What are some of the biggest challenges you’ve faced in researching the chemistry of environmental interfaces, and how have you addressed them?

One of the biggest challenges was getting people to recognize the importance of this area and our approach. My expertise in surface science and surface chemistry was typically conducted in an ultra-high vacuum on pristine single-crystal surfaces and addressed issues related to heterogeneous catalysis. I aimed to apply this knowledge to more complex environmental systems, specifically environmental surfaces and interfaces. Initially, there was skepticism that this could be done.

Doubts often manifested in the peer review process. For instance, I would submit a paper, it would be reviewed, and then I would have to revise it, sometimes repeatedly—more times than typical. However, we persevered through these challenges. Ultimately, our papers were published, and, most gratifyingly, they became highly cited benchmark papers.

Regarding grant proposals, we often heard criticisms like, “This is too complicated. You wouldn’t be able to understand anything.” Yes, it was complex, but we were able to design experiments that allowed us to learn a great deal. We, my graduate and undergraduate students, postdoctoral scientists, and I embraced these challenges, pushed forward, and paved the way in this new area of research with great tenacity.

Within your work on atmospheric aerosols, what are the most significant findings you’ve encountered in this area, and how do they contribute to our understanding of environmental chemistry?

In our research on atmospheric aerosols, we’ve developed a conceptual framework to understand the chemistry of various types of aerosols, such as mineral dust aerosols. Earth has numerous deserts and arid regions, which are likely to expand due to climate change. Once airborne, this dust can be transported at great distances, significantly affecting the particulate matter load in the atmosphere.

We have thus studied how reactions on these particles can alter their composition. For instance, we have demonstrated that calcium carbonate, a crucial mineral in regulating atmospheric CO₂, can react with nitrogen oxides to form calcium nitrate. This transformation is significant from the particle perspective because while calcium carbonate is a solid, calcium nitrate is a liquid that absorbs water and becomes an aqueous particle. This liquid state facilitates the nucleation of aqueous clouds.

We have also examined iron-containing mineral dust particles to determine how the amount of soluble iron increases when these particles react with trace atmospheric gases. This has important environmental implications as it relates to elemental cycling and the bioavailability of iron.

Additionally, we’ve researched the spectral characteristics of mineral dust aerosol in the infrared spectral range, which aids in remote sensing. NASA’s new program, EMIT, aims to determine the mineralogy of the Earth’s system to understand mineral dust aerosols better. Our data can help interpret some of the measurements they are currently making. This work underscores the broad implications of aerosol chemistry, from cloud formation to nutrient cycling in ecosystems to remote sensing analysis.

How does your research on environmental interfaces contribute to the broader conversation on sustainability and environmental protection?

Overall, our research ties very nicely into sustainability issues, as highlighted in an Environmental Science and Technology viewpoint article I co-wrote with many others in 2007 titled “Chemistry for a Sustainable Future.” In that article, we highlighted the importance of research in green chemistry and processing, energy, and environmental molecular science. Our research fits into this latter category. Understanding environmental molecular processes often allows us to determine global impacts.

Image Credit: S. Singha/Shutterstock.com

Throughout your career, you’ve developed a variety of spectroscopic techniques. Could you tell us a bit about these techniques? Which of these techniques do you believe has been most pivotal in advancing the study of environmental interfaces?

Our approach to studying environmental interfaces and atmospheric aerosols specifically leverages vibrational spectroscopy as an in situ probe to understand the chemistry involved. We conduct extensive laboratory experiments aimed at deciphering the complexity of Earth’s atmosphere. These experiments are designed around the components we believe are crucial for understanding atmospheric chemistry.

A significant factor in our experiments is relative humidity, considering the substantial presence of water vapor in the atmosphere and its influence on chemical processes. We employ various forms of vibrational spectroscopy to achieve our research goals. This includes infrared spectroscopy, where we utilize both transmission IR spectroscopy and attenuated total reflection IR spectroscopy and design/modify a variety of different types of infrared cells to do these studies.

Additionally, we integrate atomic force microscopy with infrared spectroscopy to enhance our analysis capabilities. This multi-faceted approach allows us to gain a deeper understanding of how atmospheric conditions affect chemical reactions on aerosol surfaces.

More recently, we’ve been incorporating optical photothermal infrared spectroscopy and Raman spectroscopy into our studies on environmental interfaces. These techniques, which adhere to different selection rules, complement each other and enhance our analytical capabilities based on the specific problems and length scales we are investigating. This combination has provided valuable insights into various chemical processes as well as climate-relevant properties.

Vibrational spectroscopy is particularly powerful because it probes individual molecules, ions, and specific functional group moieties, all of which have well-defined spectral characteristics. However, when these are placed in different environmental contexts, their vibrational spectra can change slightly. These subtle changes are informative as they reveal details about the local molecular environment, which influences their reactivity, light absorption, and even interaction with solar radiation in the ultraviolet region of the spectrum.

We utilize these techniques, which fall under the broad umbrella of vibrational spectroscopy, to effectively probe and understand the chemistry and dynamics at these crucial environmental interfaces.

Have you noticed an increased uptake in combining these different spectroscopies with modeling or even machine learning technologies?

Over the years, we have collaborated with theorists to understand and interpret our data better. We have also worked with atmospheric chemistry modelers to integrate our findings into their models. Additionally, we cooperate with researchers who conduct field measurements to enhance their understanding of atmospheric conditions.

As for machine learning and AI, these technologies are increasingly becoming part of everyone’s research toolkit, including ours. We incorporate them both through our modeling collaborations and in rethinking how we design our experiments.

In your Pittsburgh Spectroscopy Award Address, you will be focusing on spectroscopy as a probe for environmental interfaces. Can you give us a preview of how spectroscopy uniquely contributes to understanding these complex systems?

Yes, we recently conducted a study on sulfur oxidation chemistry, a topic that has been well-understood for decades. However, traditionally, this chemistry has been explored in the lab in the bulk aqueous phase, i.e., essentially in a beaker.

Our approach has been different. We use spectroscopic probes to examine these reactions at much smaller, micron-size scales that are more relevant to atmospheric conditions, allowing us to see how the interface influences the chemistry. We have been utilizing confocal Raman spectroscopy to study aqueous aerosols ranging from one to a hundred microns in size and observing how size affects the rates of these reactions. This has led us to incorporate interfacial chemistry into our models.

In a recent talk, I presented a lot of unpublished data, including findings on environmental DNA, which exists free in the environment rather than within cells. There is a hypothesis suggesting that if DNA adheres to surfaces in the environment, it may be protected from degradation. So, we have begun investigating whether DNA adsorbed onto mineral oxide surfaces retains its structure, specifically its typical B-form, which has a distinct handedness and structure.

Our preliminary findings indicate that the interaction between DNA and the mineral surfaces can significantly affect the DNA’s structure, and we are using spectroscopy to probe these interactions.

This is an exciting area of research for us, and we are currently drafting papers on our initial results. As we delve deeper, we’re uncovering more questions that we’re eager to explore. It’s particularly gratifying for me as this ties back to one of my first research papers, written many years ago, which also focused on the structure of DNA.

Receiving the Pittsburgh Spectroscopy Award is a significant achievement. How does it feel to be recognized in this way, and what does it mean for you personally and professionally?

At the award symposium yesterday, the experience was incredibly gratifying. As they introduced me, they read from the nomination letter, highlighting my work with accolades and accomplishments. Sitting there, listening to them, I was beaming with pride. Knowing that your peers think so highly of your research is profoundly satisfying; it couldn’t feel any better. Most importantly, it is a testament to the students and post-docs that I have worked with over the years. As the PI of the laboratory, I spend a lot of time guiding my students and post-docs, but they are the ones in the lab who make everything work and collect the spectra we analyze. What is most impressive is the labs that many of them now lead in academics, national laboratories, and industry. I am so amazed and proud of their successes and their efforts in developing and utilizing spectroscopic probes of environmental interfaces.

In your view, how does a conference like Pittcon contribute to the advancement of science, particularly in fields related to chemistry and spectroscopy?

Pittcon is an essential meeting in the field, and it has been for over 75 years. It stands at the forefront of analytical chemistry and analytical techniques. If you are looking to discover what is new in the industry, you should attend Pittcon. At the exposition, you can see all the latest tools—new software, advanced instruments, and more. It is a significant event for those in the industry as they prepare extensively to showcase their latest innovations at Pittcon.

Beyond the exposition, there are also exceptional technical talks. Pittcon uniquely brings together professionals from industry, academia, and national labs, offering a comprehensive view of the latest advancements in analytical chemistry and instrumentation. There truly is no other meeting like it.

As we mark the 75^th anniversary of Pittcon, could you share your first memory or experience of attending this conference and how it impacted your view of the scientific community?

Over the years, I have accumulated several memorable experiences at Pittcon. My first interaction with Pittcon was as a brand-new assistant professor. I had just started at the University of Iowa and decided to drive to Chicago for the conference. I was only two months into my role and was eager to explore the latest instrumentation and networking opportunities that Pittcon offered. I remember feeling quite intimidated by everything, including by the titans of the field present at the time.

Later on, I had the opportunity to be an invited speaker at Pittcon. They treated their invited speakers very well, providing not only a platform for technical talks but also organizing enjoyable social events. It was a fantastic experience.

In another year, I co-chaired a symposium with my colleague Kimberly Prather at Pittcon, also held in Chicago, which turned out to be a wonderfully successful event. Following the symposium, a promising individual approached me with his CV, inquiring about postdoctoral opportunities. Although I was not actively seeking a post-doc at the time, his resume impressed me enough to invite him for an interview. He turned out to be one of the brightest minds I have had the pleasure of working with. Interestingly, he now works for Thermo-Fisher and is most likely attending Pittcon.

Now, at Pittcon's 75th anniversary, as the recipient of the Spectroscopy Award, I reflect on these past 30 years attending the conference. It is truly remarkable to see how integral Pittcon has been to my professional journey, culminating in this significant recognition.

About Professor Vicki Grassian

Vicki H. Grassian is a Distinguished Professor and the Distinguished Chair in Physical Chemistry in the Department of Chemistry and Biochemistry at the University of California, San Diego. She is also the Associate Dean for Research in the School of Physical Sciences. Research in the Grassian group focuses on the chemistry and impacts of environmental interfaces as it relates to atmospheric aerosols, aqueous microdroplets, engineered and geochemical nanomaterials and indoor surfaces. She has developed and utilized a wide range of different spectroscopic techniques to probe these interfaces throughout her career. Her contributions have been recognized through multiple awards and honors including the 2024 Pittsburgh Spectroscopy Award, 2023 ACS Geochemistry Division Medal, 2021 American Chemical Society National Award in Surface Chemistry, 2020 Sustainable Nanotechnology Organization Award, 2019 IUPAC Distinguished Woman in Chemistry or Chemical Engineering Award, 2019 William H. Nichols Medal - New York Section of the American Chemical Society, and the 2018 American Institute of Chemists Chemical Pioneer Award. She is a fellow of several societies including the American Chemical Society, American Physical Society, Royal Society of Chemistry and the American Association for the Advancement of Science. She was elected a member of the American Academy of Arts and Sciences in 2020. 

This information has been sourced, reviewed and adapted from materials provided by Pittcon.

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