19 December 2018
Professor Holger Tost wants to find out what is going on in the atmosphere and uses computer simulations to investigate the processes influencing our climate and weather. He was appointed to the Carl Zeiss Foundation Endowed Professorship on Environmental Modeling in the Climate System at Johannes Gutenberg University Mainz (JGU) in 2016.
Particulate air pollution in cities is currently a major issue, with reports appearing in the media virtually every day, and it is also one of the main concerns of Professor Holger Tost's research group at the Institute of Atmospheric Physics at JGU. "We are currently running a project on air quality in collaboration with the environmental agency of Rhineland-Palatinate," the meteorologist explains. "We want to understand what atmospheric processes are at work, what factors we have to look out for."
He illustrates this with a particularly descriptive example: "If we want to deal with air pollution, we need to look at the atmospheric boundary layer. That is the layer of air directly above the Earth's surface." The vertical exchange between the solid and liquid elements of the Earth's surface and the atmosphere takes place there. And it is here that pollutants swirl through the air. "At night, this layer is only a few hundred meters thick, but during the day it expands to around a kilometer. This means that at night the volume of air is much smaller, and thus there is a more restricted space in which mixing can take place. Hence, air quality is worse during the night and especially in the early hours of the morning." Air quality improves during the day, because the boundary layer extends to a higher elevation and pollutants can spread across a much larger area.
"The whole thing is further exacerbated by the effects of commuter traffic. Rush hour typically occurs twice a day – once in the morning, when the boundary layer has not yet fully expanded and the blending process is not yet properly underway, and once in the evening, when the layer shrinks back again. This means you have a strong concentration of emissions in a relatively small volume of air."
Funding by the Carl Zeiss Foundation worth EUR 1,195,000
Tost uses computer simulations to explore the effects of these and other phenomena. As he speaks, he repeatedly calls up appropriate graphics on his screen in order to illustrate his points. "I deal with environmental modeling, which means 99.9 percent of my work is done on the computer," he says, pointing to the two terminals on the desk in front of him. And on he will continue with the computer constantly in use.
In 2016, he was awarded the Carl Zeiss Foundation's Endowed Professorship on Environmental Modeling in the Climate System at JGU, funded to the tune of EUR 1,195,000 over the next five years. "I was extensively involved in preparing the application," Tost remembers. "Because I was already a junior professor here at the JGU Institute of Atmospheric Physics, I was able to contribute a lot of my own ideas." For some time now, climate research has no longer been confined to the field of meteorology. There are lots of different subjects involved, from computer science through chemistry to biology. "Our field has definitely become more interdisciplinary." The professorship wants to build on this and cooperation with other research institutes will play a significant role.
"For me personally, being awarded the professorship was a major achievement," asserts Tost. It has provided him with remarkable opportunities, and not just from the funding perspective for his research. "We are able to combine aspects from a wide variety of fields in order to explore these complex climate processes. This is only possible thanks to the specific nature of the professorship."
Tost and his four-member team are working with a number of computer models, but at the heart of their research is the Modular Earth Submodel System (MESSy), which they are continuously upgrading as part of a consortium consisting of 19 partners. "All the major research institutes involved in the study of climate and weather are on board with MESSy. Nowhere else in Germany are they investigating the climate system with this level of complexity. One university alone could not possibly do that."
Particulates acting as coolants
A wide range of issues are on the group's agenda. "One of my postgraduate students simulated the Earth at around 260 million years ago, at the time when the mega-continent Pangea was still in existence." Tost pulls a dissertation paper from the shelf and flicks through some of the pages. One map shows the climate zones of the world as calculated by the computer model, while another shows the climatic conditions that can be predicted on the basis on fossil finds. Amazingly, they are almost identical.
"We are now collaborating with the Senckenberg Research Institute on a new project. They have developed a dynamic vegetation model, which deals with how plants become established, how they develop, and which substances they release into the atmosphere. I hardly knew anything about these processes before, but now we want to combine this model with MESSy."
Tost touches on a number of other topics, also mentioning the rapid increase in carbon dioxide levels in the atmosphere and conjuring up the relevant graphic on the screen. It shows that between 1960 and 2010, the carbon dioxide concentration increased by around 40 percent. Carbon dioxide acts as a greenhouse gas and heats up the Earth, with humans being responsible for the majority of the increased emissions.
"But there are also factors that can have a opposite effect. Aerosols, for example, can provide a cooling effect." Aerosols are all of those tiny particles that float in the Earth's atmosphere, man-made or otherwise. This includes the much-discussed particulates. "If we were to say tomorrow that we want to eliminate all anthropogenic aerosols, then even though we would have improved the overall air quality, it would have even more serious consequences in terms of global warming."
No-one really knows the extent to which aerosols are having a cooling effect on the Earth and its climate. In fact, there are many things that still remain unclear. For example, it is not known how aerosols interact with clouds. "This is an important research area for us, but we are still only in the early stages. Over the past few years, a lot of money has been spent on cloud seeding, the idea being to inject clouds with aerosols to suppress the formation of hail. But what we do not know is when seeding is unnecessary because a specific cloud would not have produced hail anyway. We simply do npt know enough about it."
Aerosols are an enormously complex issue. "We are talking about millions of different molecules from a variety of sources. A lot of them we can identify, as those emanating from the trees in the Botanic Garden next door look completely different to what comes out of my car exhaust, for example. But which factors should I use to different between these particles in my computer model? Their size, their origin, or the effect they have?"
In three years, the support provided by the Carl Zeiss Foundation will come to an end, although Tost is not concerned about the future of his research group. "Our work is very diverse, so I'm sure many others will be interested in us," he says. The meteorologist is in the process of submitting an application for a Collaborative Research Center (CRC) funded by the German Research Foundation (DFG). This will have the objective of improving the accuracy of weather forecasts. "Furthermore, we are also participating in various research consortium proposals, which cover topics like the composition and dynamics of the upper troposphere and issues in paleoclimatology." There will always be work to do, as long as the puzzles surrounding climate and weather remain unsolved.