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Atmospheric Sciences


The main research activities are  i) climate change research, ii) climate change and air quality interactions, iii) aerosol and environmental physics, (iv) micrometeorology and forest-atmosphere relations, and (v) dynamical meteorology.

The core of the research is the understanding of energy, mass and momentum transfer and phase transitions. Theoretical, modelling and experimental studies of nucleation, condensation/evaporation and atmospheric aerosol dynamics have continued in 2011. Studies of deposition and fluxes of atmospheric gases, cloud microphysics, atmospheric radiation, mesoscale meteorology, and climate and radar meteorology were performed.

Researchers operate together with the researchers of the Department of Forest Sciences at versatile field stations: SMEAR I (Station for Measuring Forest Ecosystem-Atmosphere Relations) station in Värriö (Lapland), SMEAR II station in Hyytiälä, and SMEAR III (urban SMEAR) in Kumpula Campus. Particularly SMEAR II has turned out to be a leading station in its research field due to its comprehensive research program and to its unique time series of fresh aerosol formation. The development and construction of novel weather radar techniques has been performed in collaboration with Vaisala Oyj. The research at the Division is also linked with the instrumental development work with international companies. The most important one has been Aerodyne Research, Inc. in the U.S.A. The co-operation concerns development of high-response greenhouse gas analyzers and the aerosol mass spectroscopy technique.

The Finnish Centre of Excellence in "Physics, Chemistry, Biology and Meteorology of Atmospheric Composition and Climate Change" started its operation in 2008. The international Master programme "Atmosphere-Biosphere Studies" has continued its operation together with the national graduate school. The Nordic Centers of Excellence CRA-ICC (Cryosphere-Atmosphere Interactions in a Changing Arctic Climate, coordinated by Markku Kulmala) and DEFROST (Impacts of a changing cryosphere - depicting eco-system-climate feedbacks from permafrost, snow and ice, Timo Vesala as a partner) started in 2010.

A project office "Integrated Land Ecosystem – Atmosphere Processes Study" (iLEAPS) has continued its work related to land-atmosphere interactions within the International Geosphere – Biosphere Programme (IGBP). The iLEAPS project aims at advancing new integrated experimental and modelling research approaches needed in the Earth System. The division is also in charge to establish national and European Integrated Carbon Observation System (ICOS).

The final report of EUCAARI (European Integrated project on Aerosol Cloud Climate and Air Quality interactions) was written in the first half of 2011. EUCAARI has 48 partners from 24 different countries and it was co-ordinated by the division. 

The researchers have co-ordinated and participated in several international projects. The researchers hosted 15 national and international workshops and conferences in 2011, organized more than 10 intensive measurement campaigns in Finland and abroad, the most important one being CLOUD (Cosmics Leaving OUtdoor Droplets at CERN).

Highlights of research

New connections between the soil and atmosphere

Public discussion of climate change typically revolves around greenhouse gases, aerosol particles, and the role of human actions, but it is just beginning to reflect an awareness of the important role played by the global nitrogen cycle. Emission of HONO from the soil is a good example of how soil processes are linked with atmospheric chemistry. It also show, how trace amounts of reactive nitrogen link the nitrogen and sulphur cycles with the water and carbon cycles. We need to document all the ecosystem-atmosphere cycles including the soil, atmospheric oxidation, and aerosol particles and their links and feedback loops to fully understand how the biosphere affects the atmosphere and the global climate. In order to do this, we need both extensive global modelling and continuous, comprehensive field measurements


Kulmala, M. and Petäjä, T. (2011) Soil nitrites influence atmospheric chemistry, Science, 333, 1586-1587, doi:10.1126/science.1211872.

Experimental observation of strongly bound dimers of sulfuric acid: application to nucleation in the atmosphere

Sulphuric acid is a key compound in atmospheric nucleation. In a laboratory setup we observed a close-to-collision-limited sulphuric acid dimer formation in atmospherically relevant conditions in the absence of measurable quantities of ammonia or organics. The observed dimer formation rate was clearly higher than the measured new particle formation rate at ˜1.5 nm suggesting that the rate limiting step for the nucleation takes place after the dimerization step. The quantum chemical calculations suggested that even in the ultraclean conditions there exist (a) stabilizing compound(s) with (a) concentration(s) high enough to prevent the dimer evaporation. Such a stabilizing compound should be abundant enough in any natural environment and would therefore not limit the formation of sulfuric acid  dimers in the atmosphere. These results show that in atmospheric conditions, clustering of H2SO4 (maybe with water and some stabilizing substances) can possibly produce a pool of clusters that are later activated for growth to climatically relevant particle sizes by e.g., sulfuric acid or supersaturated organic vapours.


Petäjä, T., Sipilä, M., Paasonen, P., Nieminen, T., Kurtén, T., Stratmann, F., Vehkamäki, H., Berndt, T. and Kulmala, M. (2011) Experimental observation of strongly bound dimers of sulphuric acid: application to nucleation in the atmosphere. Phys. Rev. Lett. 106, 228302.

CERN/CLOUD experiment: role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation

Atmospheric aerosols exert an important influence on clouds and climate.   Increased aerosol concentrations lead to increased albedo and lifetime of stratiform clouds, and to invigorated convective storms.  Model calculations suggest that almost half of global cloud condensation nuclei, CCN, in the atmospheric boundary layer may originate from nucleation of aerosols from trace condensable vapours, although the sensitivity of the number of CCN to changes of nucleation rate may be small.  Despite extensive research, fundamental questions remain about the nucleation rate of sulphuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays (GCRs) and ternary chemical species such as ammonia. Here we present the first results from the CLOUD (Cosmics Leaving Outdoor Droplets) experiment at CERN. We found that atmospherically relevant ammonia mixing ratios of 100 pptv increase the nucleation rate of sulphuric acid particles by more than a factor 100–1000.   Time-resolved molecular measurements reveal that ternary nucleation proceeds by a base-stabilisation mechanism involving the stepwise accretion of ammonia molecules. Ions increase the nucleation rate by an additional factor of between 2 and more than 10 at ground-level GCR intensities, provided the nucleation rate lies below the limiting ion-pair production rate.  We found that ion-induced binary nucleation of sulphuric acid and water can occur in the mid-troposphere, but is negligible in the boundary layer and so additional species are necessary. Even with the large enhancements in rate due to ammonia and ions, however, atmospheric concentrations of ammonia and sulphuric acid are not sufficient to account for observed boundary layer nucleation.


Kirkby, Jasper, Curtius, Joachim, Almeida, Joao, Dunne, Eimear, Duplissy, Jonathan, Ehrhart, Sebastian, Franchin, Alessandro, Gagne, Stephanie, Ickes, Luisa, Kuerten, Andreas, Kupc, Agnieszka, Metzger, Axel, Riccobono, Francesco, Rondo, Linda, Schobesberger, Siegfried, Tsagkogeorgas, Georgios, Wimmer, Daniela, Amorim, Antonio, Bianchi, Federico, Breitenlechner, Martin, David, Andre, Dommen, Josef, Downard, Andrew, Ehn, Mikael, Flagan, Richard C., Haider, Stefan, Hansel, Armin, Hauser, Daniel, Jud, Werner, Junninen, Heikki, Kreissl, Fabian, Kvashin, Alexander, Laaksonen, Ari, Lehtipalo, Katrianne, Lima, Jorge, Lovejoy, Edward R., Makhmutov, Vladimir, Mathot, Serge, Mikkila, Jyri, Minginette, Pierre, Mogo, Sandra, Nieminen, Tuomo, Onnela, Antti, Pereira, Paulo, Petaja, Tuukka, Schnitzhofer, Ralf, Seinfeld, John H., Sipila, Mikko, Stozhkov, Yuri, Stratmann, Frank, Tome, Antonio, Vanhanen, Joonas, Viisanen, Yrjo, Vrtala, Aron, Wagner, Paul E., Walther, Hansueli, Weingartner, Ernest, Wex, Heike, Winkler, Paul M., Carslaw, Kenneth S., Worsnop, Douglas R.,  Baltensperger, Urs, Kulmala, Markku: Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation, NATURE,  Volume: 476   Issue: 7361   Pages: 429-U77   DOI: 10.1038/nature10343, 2011