Graduate Student Reflections: Nathan Li

This semester, in our spring series, PCURs will interview a graduate student from their home department who either is currently a graduate student at Princeton, or attended Princeton as an undergraduate. In Graduate Student Reflections: Life in Academia, interviews with graduate students shed light on the variety of paths one can take to get to graduate school and beyond, and the many insights gained along the way from research projects and mentors. Here, Alexandra shares her interview.


As part of our Spring seasonal series, I interviewed Nathan Li, a first-year graduate student participating in the 5-year PhD program in Civil and Environmental Engineering (CEE). He completed his undergraduate studies at Johns Hopkins University, where he majored in Chemical Engineering, completing the Environmental track.

Nathan Li, a first-year graduate student in the CEE department.

After completing his undergraduate degree in 2014, Nathan spent a year working at a startup, and the year after that working in finance. However, he felt that those jobs were not completely aligned with his values—partly, he missed the learning environment of college, but he was mostly concerned about the impact of his work: “I wanted to contribute to science and technology more directly.”

In order to identify a professor you would like to work with, Nathan recommends emailing professors whose research interests you before even applying to a graduate program. It can be extremely useful to speak to the professor, in person if possible, or on the phone, to get a sense of the group and the research. “If a professor whose work you’re interested in is too busy, try to talk to one of their Ph.D. students about the group, the environment, and the research—it gives you a much better idea of what it would be like to actually work in the lab and with that professor and those students than you could get just by reading the research summary websites.”

According to Nathan, another important consideration is the length of time the professor has held his or her position. He explained that working with a more established professor generally means that you will go to work on some part of an existing project with several other group members. On the other hand, younger, less-established professors will often have much smaller groups that allow you to take the lead on your own project. “With newer professors, you’re expected to do everything more independently, but the professor also works more closely with you—more like a coworker than a supervisor.” It is important to find a group that fits your interests in terms of both research and level of guidance or independence.

Regardless of the group, graduate programs differ significantly from undergraduate life. One of the most significant differences Nathan noted was the relationship between student and faculty advisor; he mentioned that it often feels more professional and resembles that of an employee and boss. “Being able to communicate with my advisor daily via email or stopping by his office to say hi or give updates has been great. Princeton is really good at finding you mentors—that’s why I decided to come here. All the professors were nice and cared about all the students, which I didn’t feel at other schools that had larger departments.” It is very easy to get advice from professors other than your faculty advisor, as they are willing to help students outside of their groups.

Knowing that he would be working in a smaller, less established group, Nathan came into Princeton with an idea for his project already in mind. He is researching air pollution, but with a focus on trace gases that other research groups often struggle to measure precisely due to high error in data acquisition. He uses optics—infrared lasers—to detect the concentration of gases like ammonia, carbon monoxide, nitrous oxides, and methane in the air.

“Most of what we do is sampling and data acquisition, and resolving noise in the sensor detection. We work with mechanical engineers and electrical engineers to help us construct the laser-based sensors that we deploy either on towers or airplanes, and sometimes even on cars and other vehicles.” Nathan’s group, led by Professor Mark Zondlo, mainly focuses on ammonia because it is a polar molecule. Large ammonia emissions come from agricultural waste, like manure, so readings are generally taken in places where one would expect a relatively high concentration of ammonia. Thus far, his group has placed sensors in the San Joaquin valley in California, various cattle ranches and feed lots in Colorado, open areas of Beijing, and the section of the Marcellus Shale that lies in northern Pennsylvania.

Better-studied greenhouse gases like carbon dioxide are non-polar, which makes it fairly easy to measure their concentrations, but ammonia’s polar nature means that it tends to form a thin layer over the surface of the sensors. “We often have to flush it out, since it sticks to and saturates the sensors, which completely throws off our measured concentrations.” The main reason the group’s instruments are able to measure ammonia concentrations better than other labs is that they use open-path rather than closed-path lasers–the lasers are exposed to the air. “You can wave your hands through them—it’s like in the James Bond movies where they have to dodge the lasers; they’re just in the air, except they’re really low intensity so it isn’t harmful.”

Luckily, Nathan is not working alone on this project. There is also a post-doctoral researcher working with him “because I’m new and science is hard. I take on more and more responsibility for the project as I go through the program, but I definitely get help and training from older students, and I try to carry on their knowledge as they graduate and new students enter the program.”


Hearing about Nathan’s experience applying to and starting a graduate program at Princeton taught me more about how one finds their research niche, and what that can look like on a day-to-day basis. For those considering graduate school, I hope this was helpful, and I would strongly recommend speaking to current graduate students in your field of interest to learn more. To quote Nathan one final time, “the best way to learn about a research group is by speaking to the graduate students who experience it every day.”

— Alexandra Koskosidis, Engineering Correspondent