Sulphur deposition causes a large‐scale growth decline in boreal forests in Eurasia

Map of sulphur depositions for the study sites in 1980. Adopted from Savva & Berninger (2010).

Human activity has altered climate, atmospheric carbon dioxide concentrations, and the concentrations of several pollutants over the last few decades. At the same time, short‐term reactions of tree growth to climatic variations have changed during the last few decades, for reasons that are poorly understood. However, the effects of the pollutants on growth of boreal forests in these remote areas have not been quantified, but even small changes in the productivity of boreal forest should have a large effect on the carbon balance.

The growth of Scots pine, the most important forest species in boreal Eurasia, has declined by about 17% or 0.0025 mm per year from the 1930s to the 1980s in northern Eurasia. We determined this by analysing 40 tree ring chronologies north of 60°N latitude and and factoring out the age and climate effects. Although the study sites were previously considered low‐pollution pristine environments, the growth decrease was significantly related to sulphur depositions. Additionally, we observed that the sulphur depositions rendered the Scots pine forests more sensitive to drought. Although the negative effects of local pollution on plant growth have been widely observed in the past, the long-term effects of sulphur emissions and its spread to ecosystems distant from the sources of pollution have never been previously documented at such a large scale.

These results are of fundamental importance for attempts to preserve the functioning of these forest ecosystems: sulphur deposition rates are still increasing in several regions of the world including the forested boreal areas of north-eastern China and eastern Russia. On the other hand, according to the European Monitoring and Evaluation Programme (EMEP) model, sulphur deposition at 35 sites in boreal Eurasia has been decreasing with a rate ranging from 0.25 to 2.92 kg S ha-1 per every 5 years over the period 1980 to 2000. This decrease in sulphur deposition should slow down the growth decline in boreal Eurasia, but the rate of growth decline will depend upon the ability of trees to recover from sulphur deposition effects, and combination of other environmental factors, such as the frequency of droughts.

Yulia Savva* and Frank Berninger*°

*Departement des Sciences Biologiques, Université du Québec à Montréal, Montreal, Quebec, Canada
°Department of Forest Ecology, University of Helsinki

Savva, Y., and F. Berninger (2010), Sulphur deposition causes a large‐scale growth decline in boreal forests in Eurasia, Global Biogeochemical Cycles 24, GB3002, doi:10.1029/2009GB003749.




The added value of our Centre of Excellence to society


The FCoE has had a major input in land-atmosphere research on many levels and in various disciplines, such as the exchange of trace gases and aerosol particles between forests/lakes/wetlands and the atmosphere, micrometeorology, theoretical and empirical aerosol dynamics, and observations and modelling of all these in many different climatic zones from the tropics to the Arctic.

However, the effect of the FCoE does not end there; the research conducted in Kumpula and in Viikki contributes significantly to socioeconomic issues related to global sustainability and land-atmosphere-society interactions as well. Research programmes such as PEEX (Pan-Eurasian EXperiment), iLEAPS (Integrated Land-Ecosystems – Atmosphere Processes Study), and HENVI Forests and Climate Change concentrate on the effects of climate change on the environment and agriculture, forestry, energy consumption, urban planning, and extreme events. The FCoE is equipped to deal especially with questions such as sustainable managed environments and the mixed anthropogenic (sulphur and nitrogen) and biogenic (BVOCs) input to cloud and aerosol processes. The FCoE research is applied to socioeconomic issues also via the National Climate Panel chaired by Prof Kulmala; via the FCoE’s membership of the Forum of Environmental Information that produces scientific information for policy-making; and via Future Earth, the international initiative on global sustainability led by ICSU, ISSC, and UN. Yet another new avenue is opening this year, when the FCoE begins to steer the Finnish global change research towards global sustainability science co-designed by funders, scientists, and policy-makers: Prof Markku Kulmala has been elected to chair the new Finnish Global Change National Committee that will lead this development; Tanja Suni is also involved in the Committee as a Global Environmental Change programme expert.

As a major player in all these organisations, the FCoE will add value to the research conducted by its members also by advancing major global observation infrastructures such as the SMEAR and ICOS networks where the FCoE has a leading coordinative and research role; finally, the uniquely multidisciplinary composition of the group also allows a systems approach to land-atmosphere interactions from soil to vegetation and to atmospheric chemistry and cloud processes.

Tanja Suni
iLEAPS Executive Officer


Land-atmosphere interactions in urban environment

Today, more than half of world’s population resides in urban areas, and this fraction is

View off the roof top of Dynamicum showing the SMEAR III measuring tower. Photo: Antti-Jussi Kieloaho.

further expected to increase rapidly in the next decades. Thus, a growing number of people will be affected by urban climate. The ability to understand the processes leading to this specific micro-climate is crucial for sustainable urban planning and our quality of life.

In our Centre of Excellence, the Micrometeorology group has been observing the interactions between urban surface and the above atmosphere at the urban measurement station SMEAR III (Station for Measuring Ecosystem Atmosphere Relations) since 2005. We measure the vertical exchange of energy, water, carbon dioxide and aerosol particles with the state-of-the-art methodology, the eddy covariance technique, at two locations:  on a measurement mast in semi-urban Kumpula and in downtown Helsinki on top of Hotel Torni.  In addition to these continuous measurements, our group also conducts short-term campaigns to observe the land-atmosphere exchange of N2O and volatile organic compounds (VOC) in this urban micro-climate.

The aim of these measurements is to collect long time series of simultaneously measured exchange processes to develop parameterizations for various atmospheric models, and to understand the processes and their changes in time. We are interested how the different urban land use types, particularly green areas, affect the vertical exchange of different variables. For example, as a rough estimate for carbon dioxide, Annika Nordbo, Leena Järvi, Sami Haapanala, Curtis Wood and Timo Vesala recently found that if natural areas cover over 80% of the urban surface, the uptake of vegetation exceeds the carbon dioxide emissions in the source area (Nordbo et al. 2012). Thus, our measurements provide information for urban planners as well as evaluation data for air quality, numerical weather forecast and climate models.

The measurements are also part of the new Urban Boundary-layer Atmosphere Network (UrBAN) which combines a variety of different instrumentation providing data of the interaction between an urban surface and the atmosphere at different spatial scales. The network is a joint effort by the Finnish Meteorological Institute and the Division of Atmospheric Sciences. We also collaborate with groups around the world working with urban flux measurements. The near future plan is to compare the turbulent energy balance fluxes from Beijing and Helsinki using both measurements and modelling approaches.


A. Nordbo, L. Järvi, S. Haapanala, C.R. Wood and T. Vesala (2012b). Fraction of natural area as main predictor of net CO2 emissions from cities. Geophys. Res. Lett., 39, L20802, doi: 10.1029/2012GL053087

Science for decision makers

IIASA is located in the Laxenburg Castle, former summer retreat of the Habsburgs imperial family outside Vienna, Austria.

One of the largest challenges in search for solutions for problems concerning climate, environment, or poverty, is to generate a fruitful communication between scientists and policy makers. Currently, I work in the MAG group (Mitigation of Air Pollution & Greenhouse Gases) at IIASA (International Institute for Applied Systems Analysis), an institute specialising in this communication. How does this communication work? And why is IIASA heard (or is it)? In the following I list a few (possible) reasons for the important role IIASA has in the international policy arena. Note that these thoughts are mine, and they are based on my experiences only.

–        History and tradition. IIASA was founded in the middle of the Cold War, in 1972, on the initiative of US president Lyndon Johnson and USSR premier Aleksei Kosygin (the era and the participants may explain the obscure name of the institute). The goal of IIASA was to promote co-operation between East and West in interdisciplinary scientific problems too wide for national institutions to handle. After the Cold War, the co-operation was extended from the East-West axis towards global, now crossing the boundaries between the first and third world. This background gives IIASA a strong label of neutrality. As a result of this history, IIASA scientists visit Brussels regularly to report our results to EU decision-makers. Similarly, representatives of the EU member countries regularly visit IIASA to update their information on, for example, the countries’ energy production and consumption, industry, transport, related technological objectives and future development.

–        Continuous funding. More than half of IIASA funding comes from the NMOs (National Member Organizations, Finnish representative being the Academy of Finland), which typically receive most of their funding from the governments they represent. There are currently 20 NMOs, from all the continents, including the most important players (USA, Russia, China, India, Brazil, Germany, Japan, Australia). Of course, there are also NMOs that have stopped their contribution for supporting IIASA, but the typically five year long contracts are, I guess, relatively stable under the current economics.

–        Policy-friendliness. IIASA transforms its scientific results into dollars/euros and human lives. The main output of the MAG program, the GAINS emission model, for example, gives out not only the efficiency of the technologies for decreasing emissions, but also their price. Furthermore, it estimates how many human lives can be saved by paying that price. And even further, it can be set to optimize the abatements of different emissions (different in sources and pollutants) in order to achieve the maximal benefit for a certain cost. And the data is available to anyone, registration as a user is free of charge. Another example would be the ‘7 shocks and Finland’ –project, ended a year ago, which analysed how the Finnish national economy would survive the economic shock situations.

Can we learn something from IIASA to help our own research in Finland to have an influence on political decisions? Organisations with similar goals in Finland include SYKE (Finnish Environmental Institute), the new national Climate Panel (Ilmastopaneeli), and the Forum for Environmental Information (Ympäristötiedon foorumi), although the two latter do not conduct research of their own. Similarly to IIASA, these organisations have been at least partly founded by decision makers in order to aggregate information necessary for their decisions.

These organisations are necessary because the purely academic results that universities provide are often too exact or theoretical for basing political decisions on. Thus, in order to have political influence, I find researchers and other well informed agents should, firstly, support (by actively offering information and, possibly, some resources) institutions such as IIASA, SYKE, the Climate Panel and the Forum for Environmental Information which are currently responsible for refining the scientific results to a form applicable to policy. Secondly, already at university level, we should put effort in offering simplified enough versions of our results to the media and thus to have also the non-academic people to hear and understand them: if the journalists do not understand the press-releases, the results never reach the news.

Most importantly, both above points must be carried out continuously, even if results are not immediately observable: at that very moment when the majority of decision makers feel that change is necessary (and voters are ready for it), we should be able to offer updated and comprehensive knowledge on feasible options, on their effectiveness and price. I guess very few of the reports by IIASA lead to immediate decisions, but when some decisions suddenly are to be made, it is too late to start scanning through ACP, JGR or BER and discussing what could be suggested for an action.

Pauli Paasonen (Division of Atmospheric Sciences; Guest Research Scholar at IIASA)



A new book on Physical and Physiological Forest Ecology

A new book, Physical and Physiological Forest Ecology, is now available from Springer. The editors are Prof. Pertti Hari, Prof. Kari Heliövaara, and Dr. Liisa Kulmala.

This important contribution is the result of decades of theoretical thinking and high-value data collection by the University of Helsinki examining forest ecosystems in great detail. The ecology is dominated by a qualitative approach, such as species and vegetation zones, but in contrast quantitative thinking is characteristic in the exact sciences of physics and physiology. The editors have bridged the gap between ecology and the exact sciences with an interdisciplinary and quantitative approach. This book recognises this discrepancy as a hindrance to fruitful knowledge flow between the disciplines, and that physical and physiological knowledge has been omitted from forest ecology to a great extent. Starting with the importance of mass and energy flows in the interactions between forest ecosystems and their environment, the editors and authors offer a strong contribution to the pioneer H. T. Odum and his work from over 50 years ago.

This book introduces a holistic synthesis of carbon and nitrogen fluxes in forest ecosystems from cell to stand level during the lifetime of trees. Establishing that metabolism and physical phenomena give rise to concentration, pressure and temperature differences that generate the material and energy fluxes between living organisms and their environment. The editors and authors utilize physiological, physical and anatomical background information to formulate theoretical ideas dealing with the effects of the environment and the state of enzymes, membrane pumps and pigments on metabolism. The emergent properties play an important role in the transitions from detailed to more aggregate levels in the ecosystem. Conservation of mass and energy allow the construction of dynamic models of carbon and nitrogen fluxes and pools at various levels in the hierarchy of forest ecosystems.

Testing the predictions of these theories dealing with different phenomena in forest ecosystems was completed using the versatile and extensive data measured at SMEAR I and II (Stations for Measuring Ecosystem Atmosphere Relations) and at six additional stands in Finland, and five stands in Estonia. The theories are able to predict fluxes at different levels in the forest ecosystem gaining strong corroboration in the numerous field tests. Finally, the combined results from different hierarchical levels in the forest ecosystem form the physical and physiological theory of forest ecology.

Book available here


Photo of Tsukuba rice fields in summer is by iLEAPS-Japan.

iLEAPS Executive Officer Tanja Suni and iLEAPS-Eurasia Executive Officer Hanna Lappalainen travelled to the 3rd International Symposium of Arctic Research (ISAR-3) in mid-January with the aim to create new collaboration between iLEAPS, iLEAPS-Eurasia, and Japanese and Russian scientists. One of the main points of collaboration was the Pan-Eurasian Experiment (PEEX), a new iLEAPS project coordinated by iLEAPS-Eurasia at the Division of Atmospheric Sciences in the University of Helsinki.  The Finnish delegation also included Joni Kujansuu, the Finland-Asia coordinator of the Division working part-time for iLEAPS.

The delegation met five members of the Science Committee of iLEAPS-Japan in a small satellite meeting on the second evening of the conference. All the Japanese researchers present at the meeting are leading scientists in fields very relevant to either the new iLEAPS theme Sustainable Managed Ecosystems or to the Pan-Eurasian Experiment or both; Drs Takeshi Ohta, Tetsuya Hiyama, and Ayumi Kotani have more than 15 years of experience with land-atmosphere-society interactions in Eastern Siberia ( whereas Dr Kentaro Hayashi leads a large manipulation experiment on Japanese rice paddies at the Tsukuba University, looking at the influence of CO2 enrichment on carbon, methane, and, uniquely in Japan, also on reactive nitrogen cycles throughout the year (Free Air CO2 Enrichment experiment FACE; with nitrogen, FACE-N). The website of iLEAPS-Japan is now available in English as well; this will enable European scientists to keep track of the many land-atmosphere research activities in Japan especially around ASIAFLUX, where the leader of iLEAPS-Japan, iLEAPS SSC member Dr Nobuko Saigusa and iLEAPS-Japan coordinator Sawako Tanaka work actively to widen the flux measurement network in Japan, Korea, and other parts of South-East Asia. iLEAPS-Japan and coordinator Joni Kujansuu will also conduct enquiries in the Philippines in order to organise regional land-atmosphere-society activities there; one of the first steps will be an iLEAPS-ASIAFLUX early-career scientist workshop planned to take place in the Philippines in 2014.

iLEAPS IPO and iLEAPS-Eurasia would like to extend a very warm thank you for the entire iLEAPS-Japan group for a very pleasant and fruitful meeting!


Dr Nobuko Saigusa (Chair, iLEAPS SSC member)
Ms Sawako Tanaka (coordinator)
Centre for Global Environmental Research, National Institute for Environmental Studies (NIES)
Tsukuba, Ibaraki, Japan


Are diesel engines the answer in mitigating traffic emissions?

Photo: Antti Mannermaa in Tekniikka & Talous

Diesel engines are amongst the largest emission sources in urban air. The emissions consist of soot particles of about 40-80 nm in diameter. The engines emit also nanoparticles at less than 20 nm or so in diameter, consisting of various hydrocarbons and possibly also sulphur (in case of sulphur-containing fuel).

Why is it so attractive to switch to diesel instead of a less emitting gasoline engine? The answer is in fuel economy. In Finland, the national policy towards the diesel fleet has changed over the last couple of years. Today the price per liter is almost equal for both diesel and E10 gasoline. The owner of the diesel car needs to pay a monthly tax, and the savings must come from the more economical engine.

The emissions of diesel engines are rather well know and there is a continuous effort to limit the emissions even more. In 2013, the new EURO VI limits for heavy-duty vehicles will be 0.01 g/kWh for PM (particulate matter) and 0.4 g/kWh for NOx. If you compare these to the EURO I values just 20 years ago the change is dramatic: EURO I for PM was 0.36 g/kWh and for NOx 8 g/kWh. Unfortunately, the diesel engines tend to be strong and last forever, so we have to wait for a while until the fleet has majority of EURO VI level engines.

In order to cut down the emissions to EURO VI level, changes in engine technology alone will not be sufficient. This emphasises the importance of the after-treatment of the exhaust gases. Several different types of catalysts and filters exist. How well do these work? What is their efficiency? Answering these questions requires intensive research.

What makes the development towards lower emissions even more challenging is the need to consider also the effects of new type of fuels. It is possible to produce diesel fuel from biomass-based renewable energy sources, and research towards this goal is already going on. These new-generation fuels aim for a lower CO2 footprint.

I am acting as an opponent for a recent PhD thesis from Tampere Technical University that has focused on all of these aspects in a wide set of experiments. The overall message of the thesis is clear: with new technology, one can fight against particle and gaseous emissions successfully together with lower greenhouse gas emissions.

By Prof Kaarle Hämeri (aerosol physics, Division of Atmospheric Sciences)

See original blog post at The link for the press release of the thesis work can be found here in Finnish.

Mind-mapping nitrogen cycling in boreal forests

Mind-map of nitrogen cycling in boreal forests by the N group and collaborators: Dynamic nitrogen (N) pools processes in a boreal forest. Arrows stand for processes between the pools, red dots mark unknowns in the N cycle, and green dashed lines name ongoing or coming projects to solve some of the questions.

Reactive nitrogen (N) has a key role in the atmospheric chemistry and functioning of boreal forests. After years of studying the complex interactions of N cycling in boreal forests, Janne Korhonen et al. (2012) have calculated the N balance of the Hyytiälä SMEAR II Scots pine forest. The study shows that the forest ecosystem is a very efficient N recycler. Based on the new results, the atmospheric N deposition is much higher than previously estimated, and dry and wet organic deposition are important components of the total N input. However, although the pools, annual inputs, outputs and overall N cycling in the boreal forest have been resolved, new questions arise of the short-term dynamic N processes (such as amine formation via decomposition of soil organic nitrogen). These processes are important for the atmospheric chemistry and connect N even to climate effects of aerosols.

The N group at the Division of Atmospheric Sciences (Janne Korhonen, Antti-Jussi Kieloaho, and supervisors Mari Pihlatie and Jukka Pumpanen) are applying and developing new methods together with chemists, physicists and microbiologists. Current projects linking N and the atmosphere include studies on amine concentrations and fluxes, and the effect of fresh carbon input on soil organic nitrogen turnover (NITRGOFUNGI). In the future, our main focus in the nitrogen research will be to estimate reactive N emissions from soil and canopy, N transformations, and the fate of N deposited on to the forest canopy.

Contributors to the mind-map (working in the Division’s nitrogen group):

  • Jussi Heinonsalo (microbiology)
  • Maarit Raivonen (forest ecology)
  • Johanna Joensuu (forest ecology)
  • Timo Vesala (professor, micrometeorology)
  • Jukka Pumpanen (soil ecology)

Atmospheric Chemistry into the Future

During the 10th – 13th of December 2012 (the week following AGU), the 4th Atmospheric Chemistry Mechanisms (ACM) Conference (100-150 participants) was held in Davis, California, USA. The conference was spiced with delicious food, high quality talks and state-of-the-art atmospheric chemistry science, and it is definitely recommendable. Every session was concluded with a general discussion concerning the topic of the session, which gives the impression that this is more like a workshop than an actual conference. The hottest topic seemed to be Criegee Intermediates and their potentially important atmospheric reactions with SO2 to form sulphuric acid. The meeting included a special session on amines, which both counted engineering talks on how to capture CO2 using amines (this is known as CCS: carbon capture and storage) and the following emission of amines to the atmosphere due to this process and potential effects, together with more traditional talks about atmospheric amine chemistry and amines role in atmospheric aerosol formation and growth.

There was a session on isoprene (which is the most biogenically emitted volatile organic compound (VOC) with 40% of the total global emission) and HOx (=OH + HO2) measurements and the interference in these. The chemistry of isoprene has been well debated in previous years and this session also included discussion on the sources, sinks and degradation (e.g. to alkylperoxy radicals and epoxides) of isoprene and its degradation products fate in the atmosphere. Five or so years ago, recycling of OH through isoprene reactions was a hot topic. However, it seems that this source of OH is not thought to be so significant any more.

The meeting also counted sessions on gas phase precursors to SOA (secondary organic aerosol) formation including a discussion on how important the explicity of the chemical mechanism has to be in order to get something reasonable. Modellers’ favourite tools, chemical mechanism generators, were also covered with presentations on the probably most used atmospheric chemical mechanism MCM (Master Chemical Mechanism) and what we can expect of its new version (MCM 4.0). This session also included presentations on the mechanism developments of SAPRC and BOREAM (which are near-explicit mechanisms like MCM) and GECKO-A (which is a explicit mechanism). New developments in theory and experiments, future legislative drivers, investigations in Titan’s atmosphere, geoengineering and bio-energy were also presented and discussed during the meeting.


Participants from HY: Taina Yli-Juuti (atm division), Theo Kurtén (chemistry department) and Ditte Mogensen (atm division).

When money and climate put pressure on Finnish forests

Climate change is evident and we will expect that the Finnish forests will look different in the future because of increasing temperature and change in precipitation. However, forest management will also have to adapt to financial pressure. Pushed by both these drivers, forest owners will have to change their management practices by, for instance, changing the rotation period (the lifetime of the forest from planting to harvesting), the planted tree species, and the drainage of peatlands. Changing these parameters will again feed back on the climate. “Also, Finnish people have a strong connection with forests; changing the way they look or the way they can be used will stir people’s emotions. This, in turn, affects the willingness to change forest practices”, says Ditte Mogensen who is working on this multidisciplinary problem in the iLEAPS-HENVI project “Optimizing forest management and conservation to account for multiple interactions with the climate“. Other FCoE people taking part in this project include Eero Nikinmaa and Jaana Bäck from Forest Ecology, Michael Boy from our Division, and Ari Laaksonen from FMI.

The research program will, for the first time, analyze jointly all potentially important climate change impacts of forestry. Tradeoffs between the different climate change impacts and interactions between climate change mitigation and other forest uses will be analyzed. The research results have high relevancy for policy makers as we will analyse the full effects of forest management on climate change, tradeoffs between climate change mitigation and other forest services, as well as the social acceptability of climate change mitigation in the forestry.

The study is a collaborative effort between University of Helsinki department of Forest Sciences, and division of Atmospheric Sciences of department of Physics and the faculty of Social Sciences, the Finnish Forest Research institute and the Finnish Meteorological Institute.

Website of HENVI (Helsinki University Centre for Environment)

Website of iLEAPS (Integrated Land Ecosystem – Atmosphere Processes Study)

Photo of Ditte by Jari Juslin.