The high altitude research station Jungfraujoch is a half-day's journey away from Zurich, at an altitude of 3450 meters. From the mountain station of the Jungfrau Railway, tunnels through the rock bring us to the tourist attractions, panorama platform, ice palace, restaurants. A line branches off the main line and leads through a system of caves to a door carrying the sign, "No public access". Here, well concealed from the thousands of tourists, mostly from Asia, who make this excursion to the "Top of Europe", is the realm of the scientists.

Surrounded by clean air

The research station on Jungfraujoch (1) offers ideal conditions for environmental research. For most months of the year, because of its high altitude, the Sphinx laboratory, the highest point of the station, lies in the free troposphere, in other words above the emissions that make the air below opaque. This means that scientists can investigate numerous situations in a relatively unpolluted atmosphere.

Understanding the influence of aerosols

From mid-February to the beginning of April an international team of scientists were stationed at the centre working on the third campaign in the programme "Cloud and Aerosol Characterization Experiment“ – CLACE-3.

Ernest Weingartner from the Laboratory of Atmospheric Chemistry at the Paul Scherrer Institute in Villigen (PSI) (2) is head of the investigations. The aim is to arrive at a better understanding of the influence the minutest suspended particles have on our climate and well-being. The scientists examined the chemical and physical characteristics of aerosol particles and their effect of the formation on droplets in the clouds and ice crystals.

A plastic cover as an image of an ice crystal under the microscope. (Picture: Institute for Atmospheric and Climate Science at ETH Zurich) large

IInfluencing our health....

The tiny particles in the atmosphere – smaller than one thousandth of a millimetre – come from various sources. They can be made of soot, mineral dust or biological material. Aerosol particles have an affect on our health because they can nestle in the lungs from where they are practically impossible to shift.

... and the climate

But aerosols also affect Earth's climate. The fact that a major part of the solar radiation isreflected by some of them leads to a localised cooling of the atmosphere. Some aerosols, on the other hand, absorb the radiation and thus contribute to a warming of the air. The chemical composition of the particles is decisive for the affect they have on the climate. When it comes to cloud formation aerosols serve as seedlings for condensation. If the air contains more aerosols then more – but smaller – cloud droplets are formed. In turn this causes more light to be diffused into space, which also has a cooling effect.

Particularly the indirect effect of aerosols, the cooling, can act as a counterweight to warming caused by greenhouse gases. Weingartner, though, warns against overestimating this phenomenon. "The compensation only takes place over a global mean. Regionally, there are great differences." Neither is it yet clear how great the effect of aerosols really is. This is why more research is needed.

Clouds in the laboratory

A whole series of instruments were set up on the roof of the Sphinx as part of the CLACE-3-investigation in order to find some answers to unanswered questions. It's bitterly cold up there. Luckily the greater part of the scientific work is carried out inside the Sphinx at a pleasant ambient temperature. The entire space inside is filled with tubes and instruments that are connected to sundry apparatus on the roof.

For the CLACE-3-investigation the scientists used a piece of equipment for the first, time, worldwide that sucks in currents of air and separates the cloud droplets from the aerosol particles and evaporates them.

Stefan Mertes, IFT Leipzig, and Ernest Weingartner, PSI Villigen, explaining the equipment that sucks in aerosols. large

The particles are then tested for their volume, mass and chemical composition. A further method, also newly developed, makes it possible to produce an "artificial" cloud in the laboratory, using aerosole from the natural environment. Analyses lead to new knowledge and insights on the processes involved in ice crystal and cloud formation.

Platelets and needles

The "Cloud particle imager“ also sucks in ice crystals from the cloud and produces direct images of them. Thanks to these images, the crystal can be measured. Keith Bower from the University of Manchester is very pleased with last week's results. "We were able to observe the entire range of ice crystal forms. From granulates, to platelets, or needles, to wondrous hexagonal crystals." The shape of an ice crystal depends on the conditions prevailing – air temperature, humidity – in the place and at the time it is formed.

This means that the type of ice crystal can be compared to the characteristics of the clouds and aerosols that are determined by the other measurements. It is also interesting, says Bower, to take wind direction into account. Because, depending on the origins of the mass of air, different chemical compositions of the aerosols can be observed.

Plastic ice crystals

ETH Zurich is taking part in CLACE-3 with an additional project. Scientists from the group radar meteorology from the Institute for Atmospheric and Climate Science (IAC) (3) are also examining the morphology of ice crystals, but using yet another method. They spread a plastic solution on to glass slides that then surrounds the snowflakes after they land. This thin layer stays intact after the crystal has melted, thus enabling its examination and measurements with optical instruments.

Data on the shape, size and mass of the precipitation particles serve as input for precipitation models. These models help us to understand the processes of the formation of precipitation, as Raphael Schefold, PhD student at ETH explains. "We have great hopes of the model. Using the results we can evaluate meteorological radar images far more accurately."

Making the most of synergies

The results of the work from the IAC group will be collated with other results from the CLACE-3-campaign. Unique insights have become possible, especially those arising from synergies owing to the close proximity of different methods. Participants will carry out more comprehensive evaluation of the data at their home universities.

Saying good-bye to the Jungfrau

Despite the icy beauty of the surroundings – the neighbouring summit of the Jungfrau, the Concordiaplatz of the Aletsch glacier below and breath-taking view of the Bernese Oberland – one would have to get used to spending weeks on end up here. The altitude makes stair climbing strenuous and in the evening, after all the visitors have left, the connecting tunnels between the Sphinx and the sleeping quarters take on a distinctly spooky quality. No surprise then that after terminating their work at the station, some of the scientists from CLACE-3 were more than happy to take the down train to return home.

Some interesting new instruments were used during the campaign on Jungfraujoch, like the "Cloud Particle Imager“ from the University of Manchester. large