“Jump in and go for it”

ETH Fellow Nadia Shardt is researching how water droplets in clouds freeze to form ice, and the role played by particles in this process. She has developed an innovative apparatus specifically for this purpose. She hopes that her findings will enable climate models to produce more accurate forecasts.
ETH Fellow Nadia Shardt studies how dust particles in the atmosphere influence the formation of ice in clouds. (Photograph: Stefan Weiss, partners in GmbH)

Outside it is overcast, with grey clouds blanketing the sky. A strong wind gusts across the asphalt, lashing the branches of trees and shrubs and peppering heavy rain drops everywhere. Nadia Shardt, sporting a brown ponytail and wearing all black, offset by a pale blue face mask, waits at the entrance to the CHN building housing the Institute for Atmospheric and Climate Science. This is where the 27-year-old Canadian conducts her research as part of Professor Ulrike Lohmann’s Atmospheric Physics group.

Cloud from a Chip

It is only a few steps to Shardt’s laboratory on the ground floor. The blinds are shut, blocking out the poor weather outdoors. Even so, clouds and rain dominate activities indoors: Shardt is researching how water droplets form ice in clouds.

Working with Florin Isenrich, a doctoral student at the Institute for Chemical and Bioengineering, Shardt has developed a new apparatus to study this phenomenon, which they have christened a “Cloud from a Chip”. Shardt is eager to show how the invention works. Externally, it resembles a thick microscope slide, in other words a glass plate for microscopy that easily fits on the palm of a hand. Inside this, a tiny, winding system of passages produces water droplets with a diameter of around 75 micrometres. That is roughly the thickness of a human hair – and close to the diameter of water droplets in clouds.

Supercool water

The tiny droplets are embedded in oil and lined up behind each other in a row. Shardt guides the entire water-in-oil emulsion into a fine plastic tube. Arranged in parallel, these tubes form a type of artificial mini cloud. The researcher can gradually lower the cloud’s temperature with a cooling unit she has also developed herself. “At this size, pure water droplets only turn into ice at around minus 35 degrees Celsius,” she explains. Although they are literally ice cold beforehand, they do not actually crystallise. The technical term for this process is “supercooling”.

In the microscope’s black field of view, Shardt can watch around 300 droplets freezing at the same time. A camera takes images continuously. “When ice crystals form, they appear as white dots,” the chemical engineer explains. The screening process is only semi-automated at present and the image quality can still be improved, but the basic experimental approach works: "The findings tally with results from previous studies,” Shardt says.

Fun experimenting

“Developing an entire apparatus from scratch was a brilliant experience,” the scientist says. “I would never have imagined I would actually put to use so much of what I learned during my chemical engineering studies.”

Shardt specialised in thermodynamics as part of her doctorate. She is particularly interested in phase transitions. Her PhD thesis focused on theoretical problems and data from the literature. Keen to expand her horizons, she then decided to familiarise herself with the experimental side of research and “develop experiments and generate data on my own”.

Relevant for climate

She is doing just that with the new apparatus. “I'm interested in exactly how different dust particles in the atmosphere affect the formation of ice in clouds." Dust particles act as so-called crystallisation nuclei that trigger the formation of ice crystals. The scientist is therefore planning experiments in which she will mix mineral dusts, such as silicates, with the water droplets – first individually, and then in clearly defined mixtures. Her results should help to improve climate models and thus allow more precise forecasting. “It may be a tiny detail,” the postdoc explains, “But still a very important one”.

In the atmosphere, the transition from water to ice on crystallisation nuclei occurs at low- to mid-altitudes when temperatures are subzero. The process is relevant for weather and climate, because: "Ice formation changes the properties of clouds. For example, how much sunlight they let through or how much thermal radiation they retain from the Earth's surface," Shardt explains. “Or their propensity to produce precipitation”.

A heavenly view

We continue the interview in the building’s top storey. The view from the conference room is spectacular, stretching past the ETH Main Building across the whole of Zurich, over to the lake and the Alps in the distance. The sky, which appears wide and high up here, has since turned half blue, and the clouds are white, fluffy and serene.

“Sometimes I come up here to take in the view, as it inspires me to come up with new ideas,” Shardt says. She is fascinated by landscapes and the elements, which she likes to photograph during her free time: she recently took a time-lapse image of the city’s iconic Üetliberg shrouded in passing clouds. I like to explore everyday things,” she says.

Grabbing opportunities

During her Bachelor’s course, the chemical engineer realised she was interested in research. Janet Elliott, who subsequently acted as her doctoral supervisor, gave her the opportunity to participate in a research project early on. This involved ice formation as well, but in a very different context: Shardt was part of an interdisciplinary team investigating how to prevent the formation of ice in frozen transplant tissues. She had the opportunity to publish the results and present them at a conference. During the second year of her doctoral studies, she also had the chance to teach younger students, which is not common practice in Canada. She has always been open to such challenges. Her motto is: “Just jump in and go for it – and see how it goes.”

«The more we understand what happens in the atmosphere, the better we can predict the weather – and thus also make more informed decisions and find better solutions.»      Nadia Shardt

Her interest in atmospheric physics was initially fuelled by a lecture she attended during her doctoral studies at the University of Alberta, Canada. “I thought that would be an interesting topic for my post doctorate,” Shardt recalls. And a good opportunity to apply her specialist knowledge of thermodynamics. She found out that ETH Zurich is a pioneer in this field and contacted Ulrike Lohmann to “See what is possible”. And it paid off: her postdoctoral was financed by the research group’s own funds, a Canadian NSERC grant and an ETH Fellowship.

The ultimate goal: a professorship

Nadia Shardt’s goal is a professorship, and specifically one that allows her “to apply thermodynamics to relevant systems”. She is keen to continue focusing on atmospheric systems. “The more we understand what happens in the atmosphere, the better we can predict the weather – and thus also make more informed decisions and find better solutions,” she says. And she is eager to play her part in this.

As if directed to stress the relevance of research around atmosphere and climate, the weather has changed again by the end of the interview: the magnificent view has almost vanished. Wind and rain whip against the meeting room windows. It is like looking into a gigantic washing machine. But as quickly as the rain started, it suddenly stops. By the time we reach the building’s exit, the sky is blue again.