Scouting the atmosphere

If you read an article about air pollution in Switzerland, about greenhouse gases or climate change, you are most likely to find thoughts and ideas from Dominik Brunner, head of the Atmospheric Modeling and Remote Sensing group at Empa since 2006, professor of tropospheric chemistry at ETH Zurich. Involved in satellite missions of the European Space Agency ESA and in numerous international research projects, co-founder of the Swiss measurement network for greenhouse gases and much more. And honored several times for his research, including as one of Empa's very few Distinguished Senior Researcher.

How did that come about? Steadily and patiently. The topic of the environment had already interested Dominik Brunner in his youth in the 1980s, when the environmental movement emerged – with the slogan "jute instead of plastic," as he recounts with a smile, with waste avoidance, green initiatives and the attempt by "activists" at the time to join forces to put Migros – one of the largest retail companies in Switzerland and organized as a cooperative –, as cooperative members, more firmly on an environmentally friendly course.

Nevertheless, Brunner did not become a treehugger with political ambitions, but studied physics at the ETH Zurich. In his diploma thesis, he built a device for measuring hydrogen peroxide (H₂O₂) in ambient air; as a PhD student he continued with this topic – a fully automatic measuring system that was used on board a Swissair aircraft. The focus of the atmospheric scout: nitrogen oxides and ozone, which were already important environmental factors at the time.

They were to prove a door opener. The result was a publication in the renowned journal Science and an award from ETH Zurich – for the discovery that some phenomena are more widespread than previously assumed. For example, large-scale nitrogen oxide plumes in the region of the tropopause, the boundary layer above the near-Earth troposphere – caused by lightning and upward transport of air pollutants from the Earth's surface into thunderclouds.

Well, he certainly dislikes some aspects in the debate about climate change: "It's often said that researchers are just stirring up panic to get more research funding," says Dominik Brunner, "that's something that annoys me." After all, the major trends in global warming are now well confirmed – and the fact that there are unanswered questions is by no means disputed. As an example, the climate scientist mentions feedback effects: As it gets warmer, the snow and ice regions melt, especially in the Arctic – more dark surfaces, in other words, which absorb more sunlight and thus in turn accelerate global warming.

On the other hand, as temperatures rise, trees will grow in higher altitudes. The tree line in Switzerland is rising, Brunner says, and the bottom line is that vegetation is growing worldwide – and thus also sequestering more carbon dioxide. But whether such effects will balance things out in the longer term? "After all, vegetation can't migrate at will," he says, "which really worries me: We might even be underestimating the consequences of global warming."

Wouldn't that require more aggressive communication? Also speak plain language politically, like some other climate researchers? Brunner prefers to focus on his research and not to expose himself too much in public – and he doesn't enjoy arguing anyway. Press interviews, well, he gives them – "if they have to be ...", he adds with a smile.

After studying physics at ETH Zurich, Dominik Brunner devoted himself to atmospheric research in the field of nitrogen oxides, climate gases and other areas. He completed a post-doctorate at the Royal Netherlands Meteorological Institute in De Bilt and was a research assistant at the Institute for Atmospheric Science at ETH Zurich. Since 2006, he has headed the Atmospheric Modeling and Remote Sensing Group at Empa. Brunner published papers on modeling and measurement technologies and participated in satellite missions of the European Space Agency (ESA). He is professor of tropospheric chemistry at ETH Zurich and a member of numerous expert committees. Brunner received several awards, for instance, for his PhD thesis, as reviewer for ERC research grant proposals and as a Distinguished Senior Researcher at Empa.

He'd rather kick off more exciting projects like a Europe-wide measurement campaign that has just started. The EU-funded project ICOS-Cities will take a close look at climate gas emissions in large cities – in Zurich, and later also in Munich and Paris. After all, metropolises are responsible for around 70 percent of climate gas emissions worldwide, according to rough estimates. For the three European cities of different sizes, ICOS-Cities will provide helpful data – also with the help of measurements on a residential tower of Zurich's Hardau II estate, almost 100 meters high, once the city's tallest building.

In addition to conventional measurements of CO₂ concentrations, from which emissions are then calculated backwards, another method called eddy covariance is used. Thanks to extremely fast sensors, this allows records of climate gases such as CO₂, methane and nitrous oxide to be correlated with measurements of upwind and downwind conditions. This allows the "breathing" of the city to be recorded – and thus conclusions to be drawn about the causes of the emissions. And this data could in turn also reveal how road traffic, for example, affects the city on workdays or on weekends.

An appealing project for the atmospheric scout that will require ideas, curiosity and perseverance until 2025 – in the small circle of environmental scientists, not on the public stage of climate policy. And yet with practical value for people in big cities. "Climate change is certainly the Number 1 topic in atmospheric research," says Dominik Brunner, "and for me, one that is truly dear to my heart."