Fabian Mahrt – ice-cold climate research

Astrid Tomczak-Plewka

You could say Fabian Mahrt is floating in the clouds. But that would only be half the truth. Clouds - yes. Floating - no. The 30-year-old is conducting research in an area that dominated public debate until it was knocked off the top spot by the coronavirus pandemic: climate change. "I became interested in climate protection at an early age," he says. As a high school student, he was also enthusiastic about: languages, natural sciences and geography.

After graduating from high school, he took a gap year, worked in a supermarket and travelled through Southeast Asia – after that he was ready for ETH. He had concluded that environmental sciences, with insights into chemistry, biology, physics and economics, would best suit his diverse interests. "I let the different topics hit me," he recalls. He describes an introductory lecture on "Atmosphere and Climate" as a "key experience" that was to determine his academic career from then on. "From the beginning, I was fascinated by how ice crystals and clouds are formed from the smallest particles and how they can influence the climate." It may sound paradoxical to lay ears, but ice crystals can actually lead to a warming of the Earth's climate: Among other things, they are responsible for the fact that cirrus clouds become thicker and allow less heat radiation to escape into space.

In his master's thesis, Mahrt examined mineral dust with an aerosol mass spectrometer on the Spanish island of Tenerife. While aerosols of mineral origin, e.g. from Saharan dust are relatively well researched, there are major gaps in our knowledge of soot from combustion processes. The young researcher wanted to help close this gap in his doctorate at ETH by simulating the formation of ice clouds on soot particles in ice chambers, where temperature and humidity can be regulated.

Since the particles "age" in the atmosphere, he had to couple two chambers with different general conditions. The first chamber simulates how the aerosol is absorbed into the cloud, where it forms ice particles or liquid cloud droplets. The aerosols processed in this way are fed into a second ice chamber, where it is investigated how the aged soot particles influence the formation of clouds. The coupling of the two ice chambers was a technical challenge. "I brainstormed with the technicians from early morning until late at night," says Fabian Mahrt. Finally, they developed a flow tube whose temperature can be controlled and where the cloud particles change their aggregate state during transport. It took him about two years to reach his goal with this "cloud processing project".

"I am always dying to know what is going to come out"

Despite setbacks - when an instrument broke for instance - giving up was not an option for him: "I am always dying to know what is going to come out". The result is that both the specific properties of soot particles and the microphysical environmental conditions play a "decisive role" in cloud formation, thus also affecting the climate, as Fabian Mahrt's mentor Ulrike Lohmann states in the recommendation letter for the Prix Schläfli. "The award is also a recognition for the team," Mahrt says. "I would be delighted if my work has enabled me to make a contribution that others can build on."

Since January 2020, Fabian Mahrt has been at the University of British Columbia in Vancouver on a research fellowship from the European Union. The young researcher had little time to settle in: after 2 months, the lockdown was imposed in Canada as well. In the meantime, the passionate footballer has come to terms with the situation, goes jogging instead of chasing the ball and explores the nature around Vancouver. His fellowship is scheduled for three years, the third of which he will complete at the Paul Scherrer Institute. He is looking forward to that: "When I left Zurich, I left my warm nest and my social environment," he says. But it was worth it: "I can gain new experience here." "And it is great that I am getting the chance to continue my scientific work in Switzerland after my stay in Vancouver with this filled backpack."