Cloud-hunting at high altitudes

Article written by Hanne Notø, December 23, 2022

The night train brought me to Vienna in the early morning of Monday November 21. There, I was meeting my colleagues from TU Wien who were coming with me to my field campaign at Mt. Sonnblick. We set off towards the Alps, the car packed with sampling equipment, clothes for -20 C, and of course the essentials: snacks. We reached the end of the Rauris valley, but from there we could only reach the observatory at 3106 m using the gondola. The ride up was spent in complete darkness, but we could see the light of the observatory up on the top of the mountain.

The gondola taking us and the equipment up 1500 m to the observatory. The photo on the right is the observatory seen from the gondola in daylight

After arriving at the observatory we were served dinner and got to meet some of the other scientists who were there at the time. Coinciding with my stay at Sonnblick was an intercomparison campaign on cloud droplet measurements. The goal of my stay at Sonnblick was to collect cloudwater, snow and aerosol particle samples. The composition and concentrations of semi-colatile organic matter in the samples will be compared. The samples will be analyzed using a Thermal Desorption Proton-Transfer-Reaction Mass Spectrometer (TD-PTR-MS), which allows us to measure semi-volatile organic compounds in different matrices. This allows us to compare aerosol particles on filters with liquid samples such as cloudwater and melted snow. This will help better understand the transport of organic matter in the atmosphere and how it is deposited on snow, which may help the interpretation of organic matter in ice cores.

Since the location of the Sonnblick observatory is quite remote, this will allow the collection of relatively ‘clean’ samples, representing European background levels. Past studies on aerosols at Sonnblick also serve as grounds for comparison, which may help the analysis and interpretation of the data.

PM1 aerosol filter sampler. Air is pumped from the outside of the observatory and passes through a filter where particles are trapped.

Collecting snow samples from the surface

On the first morning, we set up the cloudwater sampler and aerosol filter sampler. We then made a sampling plan and decided on the division of night-shifts. The cloudwater sampling was quite time-intensive and required us to check or collect the sample every 30-60 minutes. If it was cloudy around the observatory during the night, somebody had to stay up and collect the samples.

The cloudwater sampler: air is pumped through a narrow slit and smaller particles are directed around the sampler inside (depicted on right), while larger cloud water droplets with too high momentum collide with the plate and freeze upon impact. This forms a “cloud ice cube” in the shape of the slit, which can be collected.

In the time between sampling and when it wasn’t cloudy, we tried to get some sleep and do some work. There is a hiking hut connected to the observatory, which is where we slept and ate. All our meals were prepared by the hut manager, who was kind enough to keep the hut open while us scientists were there. Normally the hut is only open in the summer months, when the mountain is accessible for hiking. In the winter it is difficult to hike in the area, and because of the snow, glaciers and cliffs surrounding the hut. We could therefore only walk on one side of it, plus the terrace on the top of the roof where the instruments were mounted. In other words, we spent a lot of time indoors. When the weather was clear, the view was incredible! I added a few photos below, but I took a couple hundred photos during my stay !!

The first few days I could feel the altitude’s effect on my body. I felt persistently tired, couldn’t sleep well for the first few nights and felt like my heart was in my throat every time I walked up the stairs. Nonetheless, samples were collected and logged, and we collected cloudwater from every cloud event that occurred. Occationally, the cloudwater sampler would freeze shut. When that happened we had to carefully remove the sample, scrape away the frost and insert a clean sampler. The longest cloud event we observed lasted 23 hours. We were sampling day and night, and collected a total of 26 cloudwater samples. During the entire campaign, a total of nearly 100 samples were collected. These samples will be analyzed in Utrecht in January 2023.

After ten days of staying in the hut, I felt quite ready to go back home to my normal routine. However, I really enjoyed my time at Sonnblick and would love to go back if given the opportunity! I would like to thank the staff at Sonnblick and the people at TU Wien who came with me just to help me collect samples, my campaign would not have been possible without them.

Auf wiedersehen!