Last autumn, researchers of the Aerosol Physics Research Group in Kuopio momentarily moved their remote offices to Puijo Tower and down to the skiing stadium. Field measurements conducted in connection with an extensive EU project will be used to study atmospheric particles and the formation of cloud droplets.
- Text Marianne Mustonen
- Photos Raija Törrönen
In Puijo Tower, cloud droplets can literally be studied inside clouds, and this is why many long-term aerosol and cloud droplet measurements have been conducted there over the years. The tower hosts the SMEAR IV station of the University of Eastern Finland and the Finnish Meteorological Institute, among other things.
“Puijo Tower is the best place for this type of research. The tower has plenty of research infrastructure readily available, so we only had to bring in devices providing us with additional information,” Postdoctoral Researcher Iida Pullinen says.
“We used the same measuring equipment up in the tower and down at a ground-station, in a container set up for measurements.”
Research groups from Germany and Sweden, and from the University of Helsinki and the Finnish Meteorological Institute participated in the measurements last autumn by sending in their instruments. Unfortunately, the travel restrictions meant that the researchers themselves were limited to remotely assisting from their home offices. Luckily, the coronavirus situation in Finland was good at the time and it was possible to conduct the measurements – which is not the case with measurements planned to be conducted in Italy this winter.
“We were still understaffed because of the pandemic. It was really hard to get all the equipment working,” Doctoral Researcher Arttu Ylisirniö says.
The study examines, among other things, the composition of atmospheric gases and the number and chemical composition of fine particles. The cloud droplet study measures the efficiency of different types of fine particles as cloud condensation nuclei
“We have access to plenty of previous measurement data from the tower, where we are constantly studying air quality,” Pullinen notes.
The air quality is still good in Kuopio, most of the time.
Iida Pullinen
Postdoctoral Researcher
Currently, the researchers are analysing and modifying the data, so that they can be used in future climate models.
“The first preliminary results have already been reported to the funder, but the processing and analysis of the data will continue and become more concise from now on. The next step is to use the preliminary results in modelling and to find ways of improving our understanding of the processes observed,” Pullinen says.
“A cloud droplet is a droplet with a size of less than 100 micrometres (1*10 ^ -6 m) in the atmosphere, of which all non-precipitating clouds are formed. A cloud droplet is formed when water vapour in the atmosphere condenses around the cloud nucleus,” the researchers explain.
“Organic and inorganic particles and pollutants in the air can serve as cloud nuclei, i.e., virtually any particle to which water vapour can condense. Without fine particles that function as cloud nuclei, the Earth probably wouldn’t have clouds.”
“One of the things studied in Puijo Tower was how well different atmospheric particles function as cloud nuclei, and which characteristics contribute to differences between them. The maximum size of a cloud droplet comes from the fact that “cloud droplets” larger than 100 micrometres in diameter generally experience the Earth’s gravity so strongly that they start falling towards the ground. At that point, they no longer fit the definition of a cloud droplet, but become hydrometeors, i.e. raindrops.”
“Many measurement results are so-called time series, especially at the time when measurements are conducted. The term ‘time series’ refers to measurement data where the desired variable, such as temperature, particle concentration or snow depth, is recorded together with the time of the measurement,” the researchers say.
"In practice, this means that the variable can be drawn in a graph as a function of time, allowing an analysis of whether any changes are observed during the measurement period. Combined with other measurement results, one can try to determine what causes the observed changes.”
“Time series can be of any length. Time series of less than one minute are used when studying very rapid chemical or physical reactions, and time series spanning several years are used when studying particle concentrations in Kuopio. Time series of the Earth’s average temperature can span hundreds of thousands of years, and they are comprised of several different time series, most of which were produced by means other than direct measurements.”
“In many disciplines, the benefits of long time series come precisely from the fact that, once the same variable has been continuously measured for several years, it is possible to observe slow changes that would otherwise drown in short-term normal variations.”
“Once again, temperature is a good example: temperature varies greatly during the year, and, for example, Christmas Eve temperatures may vary greatly between years. If measurements are conducted over decades, it is possible to analyse whether the average Christmas Eve temperature has fallen, risen or remained almost the same.”
“Long time series are also useful benchmarks for modelling experiments, which test how well our current understanding of the processes behind the variable corresponds to reality, i.e., how well modelling can reproduce the real measurement results.”
The FORCeS project, launched a year ago, will continue until 2023.
Iida Pullinen and Arttu Ylisirniö
Researchers
