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. 

Land-atmosphere research for global sustainability

iLEAPS (Integrated Land Ecosystem – Atmosphere Processes Study) is an international research programme focussing on the land-atmosphere interface. The iLEAPS International Project Office (IPO) is hosted by our Division since the start, and for the past 8 years, iLEAPS has tried to advance multidisciplinary research on land-atmosphere interactions in an international setting. Now, the IPO consists of Tanja Suni, Alla Borisova, and 10% of Magdalena Brus.

The first phase of iLEAPS (2004 – 2014) has been a time of awareness-raising and establishing a united community of land-atmosphere scientists. Science conferences held in Helsinki (2003), Boulder (2006), Melbourne (2009), and Garmisch-Partenkirchen (2011) brought to light the importance of land-atmosphere processes and feedbacks in the Earth System, and a number of publications have shown the crucial role of the terrestrial ecosystems as regulators of climate and emphasised both the long-term net impacts of aerosols on clouds and precipitation. Furthermore, the iLEAPS community has drawn attention to the importance of realistic land-use representation in land surface modelling and to that of other feedback processes and regional characteristics in current climate models and recommended actions to improve them.

Human influence has always been an important part of iLEAPS science but in Phase II (2014-2024), iLEAPS will move further towards bridging the gap between socioeconomics and natural sciences to shed light on research questions advancing global sustainability. Phase II will see the foundation of new types of research groups such as the Pan-Eurasian Experiment (PEEX) that will include large-scale, long-term, coordinated observations and modelling in the Pan Eurasian region, especially to cover ground base, airborne and satellite observations together with global and regional models to find out different forcing and feedback mechanisms in the changing climate, taking into account the simultaneous societal and cultural change. PEEX is coordinated by the iLEAPS-Eurasia Office, run by  Hanna Lappalainen and Tuukka Petäjä.

Engineering the climate can only buy time

Governments are failing to act on climate change, and greenhouse gas emissions are increasing with accelerated speed. Joonas Merikanto is studying another route to mitigate climate change, climate engineering, of which there are two main types: some methods remove carbon dioxide from the atmosphere (carbon dioxide removal), whereas others reflect sunlight back to space (radiation management).

Carbon dioxide removal methods are slow and cumbersome. Planting new forests is an option but there really isn’t enough land and, since forest is usually darker than open land, the consequences on albedo could be adverse. Fertilising certain seaweeds is another option but it would have unpredictable consequences to marine ecosystems. Engineered carbon capture would also be possible, but appears to be extremely costly compared to emissions cuts, and involves storage problems.

The reflectivity of the atmosphere could be increased by  spraying aerosol particles in the sky, where they would become seeds for new clouds or directly reflect solar radiation. Aerosols could quickly cool the planet with relative little costs. According to Joonas, this method, too, entails severe risks and unknowns. Making clouds whiter could mix up rain patterns, and particles injected in the stratosphere could turn the sky from blue to grey and possibly increase ozone layer destruction. Termination of aerosol cooling in a world with increased carbon dioxide concentrations would be problematic, as it would quickly heat the planet to temperatures above the starting point. Therefore, aerosols offer no long-term solution to climate change.

At the moment, nobody really engineers climate although some countries like China have large scale rain enhancement projects. International legislation should be developed quickly, so that individual countries wouldn’t cool the climate without consideration of consequences outside their borders. “Climate engineering is not a magical remedy. It can only be a short-term solution that would buy us time to prevent environmental crises. No matter how much we engineer the climate artificially, we still need to cut down our emissions”, Joonas says. “However, a cooler Earth that suffers from side effects of climate engineering could still be a better place to live than a severely heated planet”, he concludes.

Summary of original article (in Finnish) “Pilvi Peitoksi”, Yliopisto 10/2012, page 25.

Russell et al. (2012), Ecosystem Impacts of Geoengineering: A Review for Developing a Science Plan, AMBIO, 41(4):350-69.

Photo of Hyytiälä by Juho Aalto.

A new role for forests in atmospheric oxidation

It is commonly known that forests emit volatile organic compounds (VOC) that participate in atmospheric chemistry and, when oxidised in the atmosphere, also form new aerosol particles. Ozone, the hydroxyl radical (OH) and the nitrate radical (NO3) are generally considered to be the dominant oxidants that initiate the removal of trace gases, including pollutants, from the atmosphere. But now a new finding by Lee Mauldin IIIMikko Sipilä, Pauli Paasonen, Tuukka Petäjä, Theo Kurtén, Veli-Matti Kerminen, Markku Kulmala and their collaborators suggests that forests also participate in the production of atmospherically relevant oxidants. In a recent Nature article, the group presented atmospheric observations from Hyytiälä supported by laboratory experiments and theoretical considerations that identified another compound, probably a stabilized Criegee intermediate (a carbonyl oxide with two freeradical sites) or its derivative, which has a significant capacity to oxidize sulphur dioxide and potentially other trace gases. This compound probably enhances the reactivity of the atmosphere, particularly with regard to the production of sulphuric acid, and consequently atmospheric aerosol formation. The oxidation chemistry of this compound seems to be tightly linked to the presence of alkenes of biogenic origin. Michael Boy and his group tested this idea for Hyytiälä and Hohenpeissenberg in Boy et al (2012)Photo of Hyytiälä by Juho Aalto.

Mauldin III et al (2012) A new atmospherically relevant oxidant of sulphur dioxide, Nature 488, 193–196

Online measurement of volatile organics in Hyytiälä


Taina Ruuskanen has been working on measuring biosphere-atmosphere exchange of volatile organic compounds (VOC) for years. Originally, emissions were measured in little chambers with just one twig of a tree inside; but because VOCs participate in many chemical processes in the atmosphere and, especially, make tiny aerosol particles grow to climatically important sizes and into cloud droplets, it soon became evident that a more continuous and comprehensive observation technique is necessary. During her post-doc at the University of Innsbruck in Austria Taina worked with instrument manufacturers trying to get a new device, PTR-ToF (Proton Transfer Reaction  – Time of Flight mass spectrometer) function online with an eddy covariance system. This would allow the instantaneous and continuous observation of VOC fluxes between vegetation and the atmosphere. Taina and her group have spent the last year trying to
 make the measurement work in Hyytiälä, and this autumn they finally got good results. “Our preliminary results show that the flux method really works and I’m exited to dig out seasonal changes in the forest-atmosphere exchange of organic compounds from our one-year dataset!”, Taina says.


Ruuskanen et al., 2011, . Top: PTR-ToF in Hyytiälä for the first time; photo by Simon Schallhart. Bottom: Taina Ruuskanen in pensive mode.