RESEARCH in Jülich

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ENVIRONMENT AND CLIMATE PROTECTION

:: FLYING LABORATORIES

:: BETWEEN HEAVEN AND EARTH

:: UNDERSTANDING THE HEAVENS ABOVE CHINA

RESEARCH

in Jülich

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RESEARCH in Jülich

The Magazine from Forschungszentrum Jülich

The Earth’s atmosphere: a variety of processes in the air surrounding our planet influence the environment and the climate. Atmospheric research is increasingly concentrating on the pollutant input generated by humans.

Cover illustration: The research aircraft known as “Eco-Dimona” is a single-engine power glider. It measures the concentration of carbon dioxide and water in the atmosphere above a test area.

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Prof. Dr. Achim Bachem Chairman of the Board of Directors

Prof. Dr. Harald Bolt Member of the Board of Directors

C

limate change will have serious consequences that will endanger the basis of human life. This was confirmed by the Fourth Assessment Report issued by the Intergovernmental Panel on Climate Change (IPCC). Scientists from Forschungs- zentrum Jülich were also involved in compiling this report. The economic and intelligent use of raw materials and an eco-friendly energy supply are therefore among the most important topics for the future of our society.

The seriousness of the situation is acknowledged by almost everyone today. But how should we react to it today? Who should react? Decisive action from politicians, new products from industry, altered be- haviour on the part of consumers – all of these things are important. However, we will only succeed if we understand the complex processes in our environment in more detail. We must understand how the atmosphere, the plant world and the soil function – both alone and together.

Is the energy carrier hydrogen a friend or foe of the climate? How do clouds affect the climate? … These and many more questions have yet to be answered, and the gaps in our somewhat patchy knowledge have yet to be filled. Monitoring, understanding, acting – and in this order – is therefore our way of approaching environmental and energy research.

Using measuring instruments on the ground and in the air, environmental researchers from Jülich collect comprehensive data in international campaigns – both regionally and globally. They clarify interactions and simulate them on the basis of the processes that occur. This is how they are creating a basis for targeted and sustainable action.

For example, Jülich atmospheric researchers observed an accelerated degradation of atmospheric pollutants in the air above South China that proved very different to the process discovered in the past.

They are now clarifying this newly observed mecha- nism using simulations and experiments in the SAPHIR atmosphere simulation chamber at Jülich.

Another example: it is well known that the greenhouse gas carbon dioxide (CO₂) is absorbed by plants and soils, stored, and gradually released back into the atmosphere again. However, what interactions we can expect between these organic carbon dioxide reservoirs, different types of land use, soil moisture and the forecasted climate change – with an increase in temperature and altered precipitation – is a question that still remains to be answered. Jülich scientists are trying to clarify this. They also hope to discover how plants and plant production can be adapted to the changing climate conditions.

While these two examples focus on monitoring and understanding processes, we are close to finding applications for our knowledge in other fields. An example can be found in materials research for a future climate-friendly energy supply. Scientists from the Institute of Energy Research are developing special membranes that separate carbon dioxide in flue gases as well as new materials for fuel cells and energy-saving lamps. This topic can also be found among the articles that follow.

We hope that this edition of “Research in Jülich”

makes for interesting reading.

Prof. Dr. Achim Bachem, Chairman of the Board of Directors (right) and Prof. Dr. Harald Bolt, Member of the Board of Directors (left)

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UNDERSTANDING THE HEAVENS ABOVE CHINA

Jülich atmospheric researchers travelled to the Olympic Games in China. They drew up recommendations aiming to reduce pollution loads during the Games and made surprising discoveries on the self-cleaning ability of the atmosphere.

BETWEEN HEAVEN AND EARTH

The relationships between soils, plants and the climate are varied. Plants absorb the greenhouse gas carbon dioxide and produce substances that promote cloud formation, forests store water, and soils release different levels of carbon dioxide depending on the weather conditions. In long-term projects, Jülich researchers are investing how these things interact.

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10 :: FLYING LABORATORIES

Measuring instruments reach lofty heights on board the Zeppelin, on aircraft or in satellites. They allow atmospheric researchers to investigate the influence of trace gases and suspended particles on the atmosphere.

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3 Editorial

:: SNAPSHOTS FROM JüLICH

6 Research at a Glance

A kaleidoscope of pictures shows highlights from Jülich research – from searching for the origin of mass and dis covering changes in the brain of synesthetes to fathoming the depths of the nanoworld.

:: FOCUS

9 Understanding the Climate 10 Flying Laboratories

Measuring instruments take flight to analyse trace gases and suspended particles in the atmosphere.

13 Between Heaven and Earth

Jülich environmental scientists investigate the interactions between soils, plants and the climate.

16 Global Climate Change on a Regional Level

Interview with Prof. Harry Vereecken, Director of the Institute of Chemistry and Dynamics of the Geosphere.

18 Ice Clouds in Greenhouse Earth

Cirrus clouds composed of tiny ice crystals can have both a cooling and a warming effect on the climate.

Which effect is stronger? Jülich researchers are tracking down the answer …

20 Climate – Monitoring, Understanding, Acting 22 From Climate Killers to Raw Material Sources

Microalgae can retain carbon dioxide from power plant flue gases. They could therefore serve as renewable raw materials for the production of petrol and plastics in the future.

24 Capturing and Burying Carbon Dioxide

Filters that separate the greenhouse gas carbon dioxide in flue gases will make power plants more eco-friendly.

:: HIGHLIGHTS

26 Understanding the Heavens above China

The atmospheric chemistry above Chinese conurbations is different to what was assumed in the past.

30 Automation instead of Manual Labour

Jülich energy researchers are developing automated manufacturing techniques for fuel cells.

32 Hydrogen – Friend or Foe?

Scientists at Jülich give the all-clear.

34 Dangerous Emergency Brake for Global Warming

Sulphate particles in the atmosphere could counteract the greenhouse effect but they would also have serious side effects.

36 Light with the Right Pinch of Salt

Mercury is to be banned in energy-saving bulbs. Jülich researchers are developing alternatives.

38 News on Environmental and Energy Research

On chemical weather forecasts, world record for fuel cells, and networks for plant research.

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This magazine focuses on environmental research at Jülich.

However, this is not the only area in which Jülich scientists have scored great successes.

Research at a Glance

HELP FOR DAMAGED DISCS

If a worn intervertebral disc causes unbearable pain and non- invasive treatments do not bring relief, the disc may have to be replaced with an implant. Scientists at Jülich have helped to enhance such titanium implants. With their patented fabrication technique, the size and volume of pores in titanium can be accurately controlled, allowing them to be optimally colonised by bone cells. In recognition of this achievement, Dr. Martin Bram, Dr. Hans-Peter Buchkremer and Prof. Detlev Stöver, together with Dr. Thomas Imwinkelried from the Swiss medical company Synthes, were awarded the Schrödinger Prize worth € 50,000.

ORIGIN OF MASS

Using the Jülich supercomputer known as JUGENE, an international team of researchers has calculated the mass of the most important building blocks of matter – protons and neutrons – for the first time ever. The sophisticated simulations performed by the scientists confirmed the accuracy of a basic physical theory – quantum chromodynamics. The editors of the high- impact journal Science voted this research work one of the top ten “Breakthroughs of the Year 2008”.

LINK TIP

www.fz-juelich.de/portal/kurznachrichten

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a secondary colour perception. Scientists from Forschungszentrum Jülich and Univer- sity Hospital of Cologne used magnetic resonance tomography to demonstrate that synesthetes have an increased proportion of grey matter in the left parietal lobe (left) and in the lower right temporal lobe (right). While the brain region in the lower temporal lobe is dedicated to the perception of colour, the parietal lobe is responsible for relating sensory stimuli.

NANOSONAR

Just as sonar sends out sound waves to explore the depths of the ocean, electrons can be used by scanning tunnelling microscopes to investigate the hidden properties of the atomic lattice of metals.

This is the method used by scientists from Jülich, Göttingen and Halle to make the Fermi surfaces inside metals visible.

Fermi surfaces determine important properties such as the conductivity, heat capacity and magnetism of a metal.

included the Jülich chemist Dr. Gustav Bihlmayer, succeeded for the first time in measuring the spin of electrons in a material that exhibits the quantum spin Hall effect, which was theoretically pre- dicted in 2004. This effect could make it pos sible in future to transport information from storage media virtually loss- free and to manipulate it electrically.

BLOOD IN MOTION

Physicists from Jülich and Tokyo used elaborate computer simulations to show that when the blood flow in narrow capil- laries contains a low content of red blood cells, these cells line up in a row and take on the shape of parachutes (top). The blood cells change their shape at higher densities, lining up in two rows like a zipper (bottom). During the transition between these two states, the flow resistance of blood increases abruptly.

SIMULATING WITH PETAFLOP/S In May 2009, three new supercomputers were unveiled at Jülich for European research. The most powerful of these can perform 10¹⁵ floating point operations per second (one petaflop/s). At the time of its inauguration, it was the fastest computer in Europe and the third fastest in the world. At an official event, Federal Research Minister Annette Schavan and Prime Minister of NRW Jürgen Rüttgers emphasised the importance of supercom- puting for Germany and Europe, particularly on the international stage.

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Soil, biosphere and atmosphere influence the local and global climate.

Jülich scientists are trying to identify these factors as accurately as possible in order to understand their diverse interactions. What exactly happens in the soil, in plants and in the air? How do these processes affect the climate? How do they react to natural changes? What consequences do human activities have on them? Researchers aim to develop strategies to protect the environment and facilitate the sustainable use of natural resources.

:: UNDERSTANDING THE CLIMATE

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E

xperts estimate the number of substances in the atmosphere to be somewhere between 5,000 and 8,000. “Among these substances are trace gases which are decisive for the properties of the atmosphere, despite the fact that they often only make up around a billionth of the components in air,” says Jülich atmospheric researcher Prof. Martin Riese. A whole range of substances have a considerable influence on the climate. Over the next few decades, methane, for example, will have a short- term effect that will be just as serious as that of the greenhouse gas CO₂, which is the main cause behind climate change.

Single chemical processes can be in- vestigated in the laboratory without hav- ing to take flight. “However, the extent to which this process also acts in nature is often questionable in such instances. For example, feedback effects could be in- duced, which simply cannot be observed under laboratory conditions,” says the expert Dr. Franz Rohrer, explaining the reason behind the Jülich high-altitude flights in the polar regions, above Lake Constance, and into the centre of tropical thunderclouds. Scientists have often discovered processes during these outdoor measurements that would have been impossible to predict using laboratory studies. The best-known example is the formation of the hole in the ozone layer above the Antarctic. Chlorofluorocarbons (CFCs), which are used as coolants and propellants, were surprisingly identified as the cause behind the hole. When they escape and enter the upper polar atmosphere, CFCs are converted into ozone- depleting substances in previously un- known chemical reactions on cloud

Flying Laboratories

Satellites, research and commercial aircraft, and airships transport measuring instruments into the sky. These are then used by researchers at Jülich to analyse the influence of trace gases and suspended particles on the climate.

particles. “Moreover, meteorological processes can influence the transport of trace gases for hundreds of kilometres.

In other words, they take place on a scale that cannot be reproduced in the laboratory,” says Riese.

Looking into a coffee cup from a satellite All of this could lead us to think that atmospheric researchers actually don’t need to go anywhere at all, that they should just stay at home and concentrate on analysing the data that they receive from the measuring instruments on satellites. However, as the scientists at the Jülich Institute of Chemistry and Dynam- ics of the Geosphere (ICG) point out, the spatial resolution of such images, for example, often leaves much to be desired. Franz Rohrer, who works in ICG-2 (Troposhere), explains what scientists mean by this with the help of the cup of coffee in front of him. As he stirs in his milk, he uses it as an example:

“If you take a look at my cup of coffee from a satellite, you will only be able to

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recognise that milk has been added by the brightness of the image. However, you won’t be able to tell whether the milk has been homogeneously distributed or if streaks have formed.” Earth observation satellites do not supply continuous data from a particular region – despite the fact that the trace gas contents change over the course of a few hours or even within minutes. This is one reason why atmospheric researchers cannot do without aircraft and Zeppelins. To put it simply: they can get closer to the action.

Martin Riese and his team from ICG-1 (Stratosphere) are working to improve the visual acuity of satellite measurements. In the past, satellites could at best determine the average volume of a trace gas in a column of air that was three to five kilometres high and hundreds of kilometres wide. In cooperation with colleagues from Forschungs zentrum Karlsruhe, scientists at Jülich are developing a measuring instrument that can classify the average values of trace gases at vertical distances of less than one kilo-

metre and horizontal distances of around 50 kilometres. The instrument plays a major role in the idea behind PREMIER (Process Exploitation through Measure- ment of Infrared and Millimetre-Wave Emitted Radiation). Forschungszentrum Jülich and its European partners have proposed PREMIER as an earth observation mission with funding from the Euro- pean Space Agency (ESA) totalling € 300 million. It would begin in 2016. Up to now, the application has proven very successful. Out of a total of 24 suggestions, three have been selected for a more in- depth analysis of their scientific potential and technical feasibility – PREMIER is one of them. A similar measuring instrument for more than 15 trace gases will be tested for the first time in 2010 on the research aircraft HALO.

New research aircraft

This jet in the service of climate and atmospheric research cost € 62 million.

It conducted its first flight in Germany in January 2009. HALO surpasses all other

European research aircraft with a range of over 8,000 kilometres, a flight altitude of more than 15 kilometres and a pay- load of 3 tonnes. “With HALO, we can fly into interesting chemical and meteorological situations and study the processes there in detail,” says atmospheric chemist Dr. Andreas Volz-Thomas. The Jülich researchers are particularly interested in the tropopause, which is about five to fifteen kilometres above the surface of the Earth. The troposphere plays an important role in climate change as the changes undergone here by greenhouse gases, suspended particles and clouds have a particularly strong effect on the radiation properties of the atmosphere and thus on the temperature on the ground.

100 million research kilometres

Commercial airlines in contrast avoid

“interesting” meteorological situations, such as storms, and cannot carry tonnes of measuring instruments. Despite this, however, they can still be very success- Measuring instruments on environmental satellites (far left), on the Zeppelin NT (left) and on board research aircraft such as HALO (below) provide Jülich researchers with supplementary information on trace gases and suspended particles in the atmosphere.

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fully employed for atmospheric research.

This was demonstrated in the MOZAIC project, which was coordinated by CNRS.

Between 1994 and 2004, measuring instruments on board five long-haul Airbus aircraft took readings of the tropopause air over the course of more than 100 million kilometres. “There is no other way of recording so many data over such a long period of time. They have already been used in almost 150 scientific publica- tions”, says Volz-Thomas. One of the major findings was that the upper troposphere above East Asia contains much more carbon monoxide than expected.

The reason: forest fires and slash and burn. Satellites failed to detect the extremely high concentrations of carbon monoxide.

Once the MOZAIC project had come to a close, the long-term European observation system IAGOS-ERI was launched.

“In IAGOS-ERI, lighter easier-to-maintain and more powerful measuring instruments play an important role. They have also been authorised for retrofitting on aircraft,” says Volz-Thomas, head of the IAGOS project at Jülich. At the end of 2009, a Lufthansa machine will be fitted with the new equipment for the first time.

Discovering slowness

A flying laboratory has long been lacking for studies on the lowest atmospheric layer up to an altitude of 1,000 metres. The measuring instruments were too heavy and too large for the available research aircraft. Moreover, the aircraft flew too fast to collect near-Earth data with a high spatial resolution. As a result, a group of scientists working on the troposphere at Jülich headed by Prof.

Andreas Wahner contacted the German company who operate the Zeppelin NT:

Deutsche Zeppelin-Reederei GmbH (DZR) in Friedrichshafen. The Zeppelin NT is an airship that normally takes tourists on scenic flights above Lake Constance. It can float slowly at low altitudes, ascend and descend, pause in the air and fly with the wind whilst carrying equipment weighing up to one tonne.

“Since then, we have conducted two very successful measurement campaigns, each lasting a number of days in South Germany. During these campaigns, we determined the concentration of hydroxyl radicals, for example. These radicals are compounds that react with many pollutants, often leading to their degradation.

This is why they are often referred to as the detergent of the atmosphere,” says

Jülich researcher Dr. Andreas Hofzuma- haus (for more on the OH radical, see p. 29).

If you ask him whether he has time to enjoy the scenery during such a research mission over Lake Constance, Hofzuma- haus gives a wry smile. Nobody has time to enjoy the breathtaking sights. Instead, a mission like this means hard work for a team of many scientists: from instrument development and flight planning to data analysis. Apart from the pilot, only one researcher is actually allowed on board – the Zeppelin can’t take any more weight.

www.fz-juelich.de/portal/forschung/

highlights/zeppelin Frank Frick

The most important flight routes of the five commercial Airbus aircraft involved in the

MOZAIC project. The equipment on board measured the volume of ozone and carbon monoxide in the atmosphere among other things.

Special air-intake systems are required if scientists are to use aircraft to investigate the atmosphere. The Central Technology Division at Forschungszentrum Jülich developed this intake system for HALO. It captures highly reactive atmospheric trace substances, which can then be analysed using the measuring instruments inside the aircraft.

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Between Heaven and Earth

Forests and fields remove the greenhouse gas carbon dioxide (CO

₂

) from the atmosphere and store the carbon as biomass. Scientists speak of CO

₂

sinks. The majority of the carbon remains in the ground: in root systems, leaf litter and humus.

Soil organisms decompose the dead parts of plants and then slowly release the CO

₂

back into the atmosphere. But how much CO

₂

is swallowed or released under what conditions? Scientists at the Jülich Institute of Chemistry and Dynamics of the Geosphere are tracking down the answer.

Knowledge from the bare earth

Dr. Michael Herbst works with his two feet planted firmly on the ground. Abso- lutely nothing grows in his plot in Sel- hausen. For the last three years, Herbst and his colleagues have used environ- mentally-friendly weedkillers and cultivation practices to ensure that the field has remained this barren as part of the FLO- Watch project. The project is part of the

German Research Foundations “Transre- gio32” Collaborative Research Centre (SFB). Only decomposed plant material from the former cultivation of wheat can still be found in the field. Herbst wants to know: How much CO₂ does the naked soil release into the atmosphere? How is the flow of carbon influenced by rain or drought, snow, or a mild or cool summer?

What is the effect of a rough or fine soil

structure? In order to find answers to these questions, the scientists insert open tubes with a diameter of around 20 centimetres into the earth and measure the increase of CO₂ as well as the moisture and temperature of the soil in them.

“Temperature has the biggest influence,” reports Herbst. “But the soil organisms don’t like drought either.” How- ever, relationships exist here that the

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scientists call “non-linear”: a certain increase in soil moisture does not auto matically lead to a corresponding increase in the degradation of plant remains in the soil. If it is too wet, the soil actually emits less CO₂. “It’s as if the soil pores are blocked and gas can no longer circulate,” explains Herbst. The only way of getting to the bottom of these relationships is with many measured data from the barren field.

From the soil to the field

Normally, soils in our latitude have a more or less thick vegetation cover. How the vegetation influences the exchange between soil and atmosphere is a question that Dr. Alexander Graf and his team want to answer in the FLUXPAT project.

FLUXPAT is also part of SFB “Trans- regio32”. The scientists sink their CO₂ measurement chambers into arable land between cereal or sugar beet plants.

“The plants above the surface are therefore not of primary interest to us,”

explains Graf. What Graf is interested in, in the first instance, is what happens at the soil-atmosphere interface in a field with living roots running through it.

Dr. Uwe Rascher is interested in the vegetation itself. He tracks the photosynthetic activity of the plants with his team.

To do so, the researchers take measurements in the fields and from aircraft. In

the future, they hope to use satellites to measure the fluorescence of green plants in sunlight. The less fluorescence, the greater the photosynthetic activity and the more avidly the plants remove CO₂ from the atmosphere. Eddy covariance measurement systems record the flow of eddies above the field and measure temperature, water vapour, and the vertical CO₂ flow – in other words taken together, everything that is influenced by soil and plants. “The bottom line here is what the chamber measurements and plant measurements add up to,” says Graf.

“The results so far have agreed very well.”

“We compare different forms of vegetation cover on the one hand,” reports Rascher. “While on the other hand we want to know what effects changing environmental conditions, such as temperature, solar radiation or humidity, have on photo synthesis and the uptake of CO₂ over the course of a day.” The data are then fed into computers in order to refine and further develop models. These models will predict how global warming impacts on different agricultural crops and natural ecosystems.

Caged trees

Dr. Astrid Kiendler-Scharr looks at the relationship between vegetation and climate change from another point of view.

Her work is part of an EU project: Euro-

pean Integrated Project on Aerosol Cloud Climate and Air Quality Interactions (EU- CAARI). She does not just consider plants as the consumers of the greenhouse gas CO₂ but also as the producers of emissions that influence the climate. “Anyone

who has ever gone for a walk in a pine forest during the summer is aware that trees excrete substances into the atmosphere,” she says. “The fragrant aroma is produced from a large number of volatile substances.”

When these react with ozone and other oxygen compounds, they form particles which act as seeds for cloud formation and counteract global warming.

“Considerable disagreement exists among the experts as to how strong this effect is Anke Schickling uses a spectrometer to measure the solar radiation reflected by the surface. The “Eco-Dimona” research aircraft can be seen in the background measuring the concentration of water and carbon dioxide in the atmosphere.

Astrid Kiendler-Scharr uses experiments in plant chambers to determine what substances plants emit into the air.

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– the estimates differ by multiples of ten and a hundred,” says Astrid Kiendler- Scharr.

In order to learn more, the scientist places small trees in large glass containers in cooperation with colleagues from the plant institute. This allows Kiendler- Scharr to measure what the plants emit, how particles are formed from these emissions, and how plants are affected by stress caused by heat, drought or parasitic attacks. “Higher temperatures, for example, tend to cause an increase in the amount of emissions from trees and therefore in aerosol formation,” reports the researcher. Global warming could therefore simultaneously lead to cooling by aerosols.

A forest under surveillance

Dr. Thomas Pütz is far from satisfied with single trees. His investigations focus on an entire forest: the watershed at the top end of the Wüstebach catchment in the Eifel National Park. It is also part of the Rur observatory: a large area measuring 2,400 square kilometres along the River Rur, which is being monitored as part of the long-term project TERENO (see box on p. 17).

After the end of the war, spruce trees were planted in the Wüstebach catchment for timber production. The forest is now to be converted into a site-adapted

mixed forest. However, the implications of this project are still unclear: How much carbon dioxide and nitrogen will be stored or released beforehand and after- wards? How will the water budget and flora and fauna change? “We couldn’t believe it when we discovered that no studies have actually looked at such a restructuring measure in an interdiscipli- nary way,” says Pütz.

Together with his colleagues from Jülich, as well as those at the universities of Trier, Bonn and Aachen, he is helping to bridge this gap in knowledge. Since 2007, scientists have been planting a network of soil sensors in an area measuring 27 hectares to allow them to measure soil moisture, for example, at different depths. In the middle of the forest stand, there is a rain radar device and a weather station. The CO₂ emissions of the forest floor are registered at different measurement points, as is the volume of carbon compounds in the water. The scientists count and determine the types of animals and plants and estimate the biomass in the ecosystem. In what are known as lysimeters – metal cylinders that are open at the top and contain extracted blocks of soil measuring around 1.5 cubic metres – sensors that are connected to a computer via a wireless network monitor water and mass transport in real time.

By the time the first spruce trees are felled, an inventory will have been drawn up which will allow changes to be recorded. “We assume that the forest floor will emit a lot of CO₂ immediately after tree felling, and that it will take several years after reforestation before the forest will once again function as a carbon sink,”

says Pütz. The exact process is the subject of debate and can only be clarified when the data are available.

Only the combined results of all of these projects will offer a comprehensive explanation of how climate, soil and plants influence each other.

Wiebke Rögener The fluorescence of a leaf is being meas-

ured here. From this, the photosynthetic activity of the plant can be determined.

Extracted blocks of soil in lysimeters help us to understand the role played by water and soil structure in the transport of sub- stances and the impact of climate changes on these processes.

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An Interview with Professor Harry Vereecken

Global Climate Change on a Regional Level

How is climate change affecting Germany? What ecological and economic consequences does it have in the different regions – from the North German Plain to the Alps? Finding the answers to these questions is the aim behind the project entitled Terrestrial Environmental Observatories (TERENO). Prof. Dr. Harry Vereecken, Director of the Institute of Chemistry and Dynamics of the Geosphere at Jülich, coordinates the network of six Helmholtz centres together with his Jülich colleague Dr. Heye Bogena.

Question: There are a plethora of climate monitoring stations – what’s so special about TERENO?

Vereecken: What is unique is that we are intensively monitoring all components of the terrestrial system – soil, groundwater, plants, and atmosphere – in four regions of Germany. This is the first time that such a large and diverse landscape is the

subject of a long-term and interdiscipli- nary investigation. The observation area for which Jülich is responsible, namely the Rur observatory, stretches from the Eifel National Forest to the Lower Rhine Embayment and is as big as Luxembourg.

We will collect data here for a period of at least 15 years – on the greenhouse gas carbon dioxide (CO₂) and the climate, as well on the nitrogen budget, methane formation, water and soil quality and on biodiversity. At the same time, we will analyse the land use. What are the consequences of reforestation or open-cast mining? Will farmers have to water more in the future? Up to now, there have not been enough data available to answer this question.

Question: What knowledge gaps are particularly serious?

Vereecken: We know very little about processes in the deeper soil layers. And yet they play an extremely important role in terms of the climate. This is where a large proportion of bound carbon is stored – globally estimated to be around

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1,600 billion tonnes. It is therefore es- sential that we find out how fast it is converted and released back into the atmosphere as CO₂, and how temperature increases or changes in the water budget affect this process.

Question: How do you acquire such information?

Vereecken: We employ a variety of different methods – from remote sensing using satellites and radar stations to sondes in the soil and lysimeters. Lysimeters are extracted soil cores measuring around 1.5 cubic metres in metal containers that are open at the bottom and allow us to precisely measure the transport of water and substances. Within the framework of SoilCan, a TERENO subproject, a total of 120 lysimeters are being installed in the four observatories. All measured data are transmitted via wireless networks and monitored in real time.

Question: Basically, we’re talking about blocks of soil in large tin cans – what can you discover with them?

Vereecken: Among other things, lysimeters can be transported to other sites both within and between the observatories – for example, from regions with a lot of rain to regions with low precipitation or from cooler to warmer regions. This allows us to observe what happens, for example, when grassland soils or arable soils in the Rur observatory are subjected to greater drought, as is common in East Germany. In this way, we can simulate future climate changes.

Question: Why do the measurements take so long?

Vereecken: 15 years is actually a short period of time for such studies. It takes hundreds of years to break down stable carbon compounds in the soil. Although we don’t want to study weather fluctua- tions of individual years, we do want to study the development and impact of climate trends in the long term. This is why it’s important that TERENO is connected to other long-term research projects, for example the EU Network of Hydrological Observatories (NOHA), The TERENO project comprises a national German network for observing the Earth.

From the North German Plain to the Alps, environmental changes are being studied in four different climatic regions (observatories).

TERENO – the Facts

The national network of observatories is operated by six centres in the Helm- holtz Association: the German Aerospace Centre, Forschungszentrum Karls- ruhe, Helmholtz-Zentrum München, Helmholtz Centre for Environmental Research, Helmholtz-Zentrum Potsdam, and Forschungszentrum Jülich, which has taken on the role of coordinator. The project will initially run for a period of 15 years and has been granted funding by the Helmholtz Association totalling

€ 12 million over the next three years. Additional funding will be made available for subprojects: for example, the lysimeter network SoilCan (€ 3.6 million) and TERENO-ICOs, which will measure trace gases (€ 2.75 million). Work began on setting up the network in 2007 and the programme was officially launched at the end of 2008. www.tereno.net

which aims to record the water budget in a large number of European regions. Our work in the Rur observatory is also directly connected to the “Transregio32”

(TR-32) Special Research Centre in which Forschungszentrum Jülich is cooperating with the universities at Cologne, Bonn and Aachen. TR-32 uses the same infra- structure that is made available by the Helmholtz Association.

Question: Can you use all of this to look into the future?

Vereecken: If we combine satellite data, detailed measurements on precipitation and soil moisture with information on the groundwater level, for example, we will be able to predict more accurately than today whether there is a danger of flood- ing. We will use the coupled measurement data to further develop models that will allow us to make better regional pre- dictions on climate change and the ecological and economic consequences that we can expect.

Interview: Wiebke Rögener

Northeast German Plain Observatory

Harz/Central German Plain Observatory

Bavarian Alps/Foothills of the Alps Observatory Eifel/Lower Rhine

Embayment Observatory

Uecker Catchment Area

Rur Catchment Area

Ammer Catchment Area

Bode Catchment Area

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Ice Clouds in Greenhouse Earth

Scientists from Jülich meticulously measured the ice water content of cirrus clouds and thus improved our understanding of the role of these clouds in the climate system. In addition, they discovered something surprising about the organic aerosols that play a role in the formation of clouds.

A

horse gallops over the ice in Greenland. It is accompanied by an ice cloud that is up to 50 metres high at times. When polar researcher Alfred Wegener observed this on an expedition back in 1911 and 1912, he concluded that air can be “ice-super- saturated”. This means that the air contains more water vapour that it actually should. The excess water only crystallises

to ice – depending on the prevailing temperature – when it meets particles or droplets in the air. As the horse releases these particles with its moist breath, a cloud out of ice crystals instantaneously forms. The phenomenon of ice-supersaturation first described by Wegener is the subject of recent atmospheric and climate research to which Jülich scientists have contributed new findings.

Clouds at an altitude of between six and twenty kilometres, consisting solely of ice crystals, influence the heat balance of Earth. On the one hand, they reflect incident sunlight back into outer space.

On the other hand, they decrease the emission of heat from the Earth’s surface into the cosmos. “Cirrus clouds can therefore have both a cooling and a warming effect – what the overall balance looks like is still unclear,” says Dr.

Martina Krämer, head of the “Cloud”

group in ICG-1 (Stratosphere) at Jülich.

For the Intergovernmental Panel on Climate Change (IPCC), the “feedback”

between global warming and the climatic effects of clouds is a major uncertainty factor in all projections: Will cirrus clouds, which usually appear as fluffy white clumps or strips, heat “greenhouse Earth” even more? Or will they help to lower the global temperature increase caused by mankind?

Better climate models

To answer this question, we must first determine the conditions under which cirrus clouds are formed. Jülich scientists have developed sophisticated instruments to determine the water vapour content of ice clouds and in clear skies, and have already used them in over 100 research flights above the tropics, the Arctic and in the middle geographic

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latitudes. “We have acquired a quality- controlled data set that is unique in terms of its size and also contains cirrus clouds at extremely low temperatures down to - 90 °C,” says Krämer’s colleague Dr. Cornelius Schiller, head of the “Water Vapour” group. The measurements show that the density of the clouds – crucial for the reflection of radiation – and their ice water content decrease rapidly with increasing altitudes and simultaneously decreasing temperatures. Furthermore, the researchers determined the extent to which isupersatu- ration occurred inside and outside the ice clouds. “Our data are already being fed into climate models and allow us to simulate the formation of cirrus clouds more realistically on computers,” says a satisfied Schiller. The Jülich researchers

also discovered that the measured high supersaturations fitted the number of ice crystals in the clouds, registered by scientists from Mainz on some of the flights. This number was unexpectedly low in the tropics, meaning that in this climate-sensitive region, the ice crystals absorb less water than was previously assumed.

Ageing substances and aerosols When searching for an explanation, it is important to know the following: even in the upper troposphere, water vapour only crystallises to ice – as observed by Alfred Wegener close to the ground – because of the suspended particles present there. These aerosols can be of a very different chemical nature and comprise substances such as sulfuric acid, black

carbon or mineral dust. “One assumption is that aerosols actually contain more organic material than was thought and therefore are comparatively poor ice crystallisation nuclei ,” says Krämer.

This puts the research conducted by scientists at ICG-2 (Troposhere) in a whole new light. They are actually studying these organic aerosols as part of the European Integrated Project on Aerosol Cloud Climate and Air Quality Interac- tions (EUCCAARI) because they are nuclei for water clouds. “All of us have felt the cooling effect of these clouds at some point,” says Dr. Thomas Mentel, head of the “Aerosol” section. Water clouds in the lower few kilometres of the atmosphere are important antagonists of global warming caused by greenhouse gases.

Scientists at Jülich are investigating how organic aerosols are formed and why there are so many of them in the atmosphere. It is common knowledge that trees emit volatile substances referred to by chemists as terpenes. Aerosols are formed from these together with ozone and other oxygen compounds under the effect of sunlight (see also “Between Heaven and Earth”, p. 13). In the SAPHIR atmosphere simulation chamber, researchers at Jülich have reconstructed this process. In doing so, they discovered that the volume of aerosols formed was significantly underestimated when only the direct reaction of terpenes was taken into account. The oxidation products cre- ated from the terpenes also form aerosols days later. “We are hot on the heels of the missing sources of organic aerosols,” says a convinced Mentel.

Frank Frick A child’s freezing breath makes a phenomenon visible that still puzzles atmospheric and

climate researchers: the supersaturation of air with water vapour.

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5

6 7 1

Climate –

Monitoring,

Understanding, Acting

Using a variety of devices and methods, Jülich

scientists are studying different factors that influence the climate. The aim is to understand these processes in detail and to derive recommendations for climate protection measures from them.

2

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9 3

8 10 4

1

Clouds can have both a cooling and a warming effect on the climate.

2

The Zeppelin carries measuring instruments up to altitudes of 1,000 metres.

3

Environmental satellites deliver ever more accurate measurements of trace gases in the atmosphere.

4

The high-altitude research aircraft HALO can carry up to three tonnes of measuring instruments.

5

Such membranes are used to “sift out” carbon dioxide from flue gases.

6

Fuel cells deliver eco-friendly energy.

7

Algae consume carbon dioxide and can be used as a biofuel.

8

A radiometer measures the moisture content of soil.

9

Fluorescence is used to determine the photosynthesis rate of a plant.

10

Lysimeters supply environmental information from the ground.

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C

arbon dioxide or CO₂ for short is a greenhouse gas and is regarded as the most important cause of global warming. “But we shouldn’t forget that it has another side,” says plant researcher Prof. Ulrich Schurr, Director of the Jülich Institute of Chemistry and Dy- namics of the Geosphere. After all, CO₂ is vital for life on Earth. Above all, green plants require the gas for photosynthesis.

They use it together with sunlight to produce sugar molecules, which they need to store energy and as structural material to grow leaves, stalks and stems.

Already today, around 10 % of all products in the chemical industry are based on plants – a figure that is set to rise significantly in the future. The reason is:

Crude oil, which is used as a source of petrol, synthetic materials and medica- tions, is becoming scarce. In addition, products based on plants are much more eco-friendly. At the end of their lifetime, plants only release the same amount of CO₂ into the atmosphere as they absorbed from the air during their growth period.

From Greenhouse Gases to Raw Material Sources

Carbon dioxide (CO

₂

) can also be put to good use. It can be used to “feed” algae that then function as a source of chemical products and provide energy in the form of biogas or biopetrol. Scientists at Jülich are applying their know-how at the most advanced algae breeding plant in the world for efficient carbon conversion at the RWE power plant Bergheim-Niederaußem.

The surfaces on which plants grow however – forests, plantations or arable land – cannot be expanded at will. Fuel manufacturers and the chemical industry are already competing with the food industry today for the limited crops available. One way out of this dilemma is to produce biomass, which is not used as a food. “The aim is to produce as much biomass as possible in a short period of time without using large amounts of our precious water or high-quality arable land,” explains Schurr.

Algae don’t need a field

Microalgae are promising candidates for biomass production: their growth rate is seven-to-ten times higher than that of land plants. They can also be cultivated in closed facilities, thus allowing sites to be used where the soil is unsuitable for plant cultivation. Salt-water algae, like those being studied by scientists at Jacobs University Bremen, for example, are particularly appropriate. While fer- mentation and rotting processes occur easily in freshwater, the microorganisms Scientist Thorsten Brehm analyses the

mixture of salt water and algae in the plastic tubes in the pilot plant in Nieder- außem.

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responsible for these processes don’t feel at home in salt water. In cooperation with the scientists at Bremen and the energy company RWE, Schurr’s team has decided to focus on improving the production of salt-water algae and studying the usage potential of the resulting biomass.

The power supply company RWE put a 600-m² pilot facility for algae cultivation into operation in November 2008. The algae in this facility are “fed” directly with flue gas originating in the neighbouring lignite-fired power plant Niederaußem.

The flue gas is first directed into what is known as a bubble reactor. This contains a mixture of salt water and algae, which

absorbs carbon dioxide from the flue gas until it is saturated. The remaining gas therefore contains less CO₂ and is released into the air via a stack. The carbon-rich mixture of algae and salt water is fed from the bubble reactor into a greenhouse with transparent, V-shaped plastic tubes. This is where the algae grow. They are harvested simply by filter- ing them out of the salt water. The facility produces up to 6,000 kilograms of algae per annum and requires 12,000 kilograms of carbon dioxide from flue gas to do so.

Clever control systems

Parallel to the ongoing algae cultivation in Bergheim-Niederaußem, Schurr’s research team is also working on making production more efficient. Their point of departure: in addition to carbon dioxide, nutrition and light are important for the growth of algae as is temperature. This is the motivation behind the clever control strategy pursued by the scientists. Sen- sors take regular contact-free measurements of the condition and growth of the algae. The level of CO₂ and nutrients can then be automatically adapted depending on the data acquired in order to ensure optimal thriving conditions for the algae.

By measuring the chlorophyll fluorescence, the scientists can determine how

“fit” the algae are. The more actively the algae carry out photosynthesis, the more energy is set free by the chlorophyll responsible for this process. This energy is

released in the form of a measurable flu- orescent light signal.

Furthermore, Schurr’s team of researchers are investigating the effect that the innovative roof of their small greenhouses in Jülich has on algae production. It is constructed from highly transparent glass panels through which UV radiation and particularly large quan- tities of light can pass into the facility.

The spectral composition of this light is almost identical to that of natural sunlight. The scientists are also checking to see if the tubes in which the algae grow can be further improved.

“All of our findings combined will hopefully increase production in the algae facility in Niederaußem,” says Schurr.

The plan is to equip the plant there as deemed necessary step by step. The Jülich scientists are convinced that their research work will confirm that algae cultivation and the recycling of biomass, whether for use as fuel or as construc- tion materials, are worthwhile – for the environment and also for the economy.

Frank Frick

Microalgae produce biomass in plastic tubes and consume carbon dioxide in doing so.

Photosynthesis activity in different algae samples: the algae in a fresh suspension (centre) adsorb the most CO₂ compared to a diluted (bottom) and a precipitated mixture (top).

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T

he Intergovernmental Panel on Cli- mate Change (IPCC) predicts an increase of up to 6 °C in the average temperature on planet Earth by 2100 – depending on the assumed scenario. The main reason for the temperature rise since the middle of the 20th century is the increasing concentration of CO₂ in the atmosphere. It has increased from a preindustrial value of 280 ppm (parts per million) to 379 ppm in 2005. Germany

and the European Union are campaigning to limit the envisaged temperature rise to a maximum of 2 °C. However, this can only be achieved by combining several different measures. In addition to the increasing use of renewable energy sources, the German Federal Government is therefore also calling for the development of coal-fired power plants that emit almost no carbon dioxide into the atmosphere.

The idea is to store the gas in underground reservoirs instead. The National Research Centre for Geosciences in Potsdam is currently working on a pilot project in the town of Ketzin in Brandenburg, which involves injecting a total of 60,000 tonnes of carbon dioxide into a saline aquifer between 2008 and 2010.

“This carbon dioxide comes from the chemical industry and is transported to Ketzin by truck,” explains Dr. Petra Zapp, who works as a process engineer at Jülich. The reason why the gas does not come from power plants is simple: there is no efficient process for capturing the carbon dioxide in the flue gas emitted by power plants. “Currently, the best developed separation technique for conven- tional power plants is chemical scrubbing,” says Dr. Wilhelm Meulenberg, who like Zapp works at the Institute of Energy Research. This “scrubbing” involves bind- ing the carbon dioxide chemically to a solution and then releasing it again before transport by increasing the temperature. However, all of this costs energy.

Capturing and Burying Carbon Dioxide

Carbon dioxide (CO

₂

) must be prevented from entering the atmosphere.

Researchers at Jülich are developing membranes to separate this gas that

is harmful to the climate from the flue gas in coal-fired power plants so

that it can then be stored in underground reservoirs.

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“The efficiency of a power plant drops by more than 10 percentage points as a result,” says Meulenberg. “An average coal- fired power plant in Germany has an efficiency of around 38 %, which means that this is a huge loss.”

Reducing this energy loss is the aim of the MEM-BRAIN research project involv- ing Forschungszentrum Jülich as well as other German and European research centres and universities together with partners from industry. The MEM-BRAIN project is headed by Prof. Detlev Stöver, Director of the Institute of Energy Re- search. Instead of using a chemical process that consumes energy, the aim is to

“sift out” the carbon dioxide from the flue gas using membranes. Furthermore, the scientists are also designing suitable efficient power plant concepts. Within the MEM-BRAIN collaborative research programme, Forschungszentrum Jülich is responsible for developing membranes from ceramic materials. However, the development of materials alone is not enough. “The membranes have to be adapted to suit different types of power plants and they must function efficiently in these plants,” says Meulenberg. “The major advantage here at Jülich is that we have everything under one roof. We are

developing the materials and the membranes; my colleague Dr. Torsten Markus tests them under power plant conditions.” Zapp continues: “And we keep the system as a whole in mind and evaluate it. We perform life cycle assessments, for example, on future coal-fired power plants equipped with membranes and look at all of the environmental impacts involved in constructing and operating the power plant.” Needless to say, the costs also play a role. Meulenberg:

“When we discover a new material for membranes, it is not unusual that our colleagues will then say something along the lines of: ‘Your material is great, but how are you going to pay for it?’”

While Zapp has the more thankless task of taking the wind out of her colleagues’ sails before they invest too much work in the development of membranes that don’t make ecological or economic sense, other researchers come

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SP750 SP650 SP550 SP450

to Meulenberg with specific requests. His colleague Dr. Ernst Riensche, for example, is modelling membrane modules to find the optimal operating temperatures and pressures as well as the best way of integrating them into a power plant.

Meulenberg then looks for a membrane material that can withstand the ambient conditions that Riensche requires.

Researchers at RWTH Aachen University offer additional support. They use computer models and measurements to simulate the mode of operation of a membrane on an atomic level. The researchers at Aachen also plan to test the membranes in a large demonstration plant.

www.co2separation.de Axel Tillemans

The temperature rise on Earth depends on a number of factors including the concentration of carbon dioxide in the atmosphere.

The curves represent different political scenarios. The blue curve assumes that the maximum annual level of carbon dioxide emis- sions will be reached around 2020. Although emissions are to be drastically reduced, the concentration in the atmosphere will remain constant for the next century at 450 ppm. In the other scenarios, maximum emissions will be reached at a later stage.

The carbon dioxide concentration that remains constant over a number of centuries is therefore higher. The red curve (1,000 ppm) represents an increase of 5.5 °C in the average global tempera- ture, while the blue curve signifies an increase of 2.1 °C in the average temperature.

As they are composed of many layers, membranes combine different properties:

stable large-pored ceramics ensure mechanical strength, while dense fine- pored ceramics function as a filter for gases.

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D

inner: “Hotpot with well seasoned fish cooked not on burning embers (carbon dioxide emissions!) but on an electric hob,” notes Prof. Andreas Wahner on 10 August 2008 in his blog.

After all, the Director of the Institute of Chemistry and Dynamics of the Geo- sphere (ICG) at Forschungszentrum Jülich came to Beijing with his team to conduct studies to improve the quality of the air.

The German-Chinese cooperation for better air began back in 2006. Scientists from ICG travelled to China where they conducted two large measurement campaigns between July and September to analyse the quality of the air. In cooperation with colleagues from the Leibniz Institute for Tropospheric Research in Leipzig and teams of scientists from China, Taiwan, Japan and Korea, they analysed the pollutants in the blanket of smog over two Chinese megacities:

the urban areas around Beijing and Guangzhou in the Pearl River Delta where millions of people live and work. They also studied the self-cleaning ability of the atmosphere above these megacities.

Industry and air pollution growing China’s booming economy, increasing industrialisation and the ever heavier traffic have undesired side effects. The air is being increasingly contaminated with pollutants such as ozone, particulate matter, hydrocarbons, nitrogen oxides and carbon monoxide. For example, the lower layer of the atmosphere (the troposphere) above China already contained 50 % more nitrogen dioxide in 2002 than it did in 1996. The researchers want to use their analyses in the “Care Beijing” campaign to determine what substances are polluting the atmosphere, how they can be decomposed, and what chemical and physical processes are

Understanding the

Heavens above China

Athletes were not the only group of people who spent years preparing for the

Olympic Games in Beijing. Scientists from Jülich were on site two years before the

sporting event even began. In August 2008, they returned to China once again for

the Games. Their goal: to ensure clean air for the Olympic competitors and to study

the atmospheric chemistry in the Chinese conurbations.

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behind the transport and degradation of the pollutants. The findings could also be interesting for other megacities.

The Jülich scientists used their measurements to draw up specific recommendations for their Chinese partners in the run-up to the Olympic Games. The main aim was to reduce the pollution levels of particulate matter and carbon monoxide during the Games. The recommendations of the atmospheric researchers included repairing leaks at petrol stations and refineries and using sulphur- free diesel fuel. The scientists did not believe that a ban on the use of cars would actually lower the concentration of nitrogen oxides during the Games.

Imposing early constraints on industrial plants appeared to be more efficient.

“We worked well with the Chinese side,”

says Wahner. “The government in Beijing used our measurements and calculations as a basis for their plans.”

Advice for athletes

The Jülich expertise was also put to good use for the German Olympic preparations: the German Olympic Sports Association and the Federal Sports Research Institute refer to the ICG studies in their brochure containing medical advice for athletes travelling to Beijing. Their recommendations to athletes to train predominantly in the

morning and evening in China were partially based on measurements of the temperature and of ozone concentrations taken by the Jülich scientists in 2006.

During the Olympic Games, the Jülich scientists provided daily reports for the athletes on air pollution. Some of the measurements for the reports, for example, were taken of diffused sunlight on the roof of Peking University. “We used these measurements to determine the distribution of aerosols, nitrogen oxides, ozone and formaldehyde,” explains Wahner. The campaign was con- tinued after the Olympic Games were over in order to determine whether the

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measures implemented by the Chinese authorities on the recommendation of the scientists were effective.

For comparative purposes, the researchers recorded the concentration of pollutants during and after the implemen- tation of these measures. A location around 80 kilometres southwest of Bei- jing was also included in the study. The measurements showed that the level of pollution dropped by 30 – 50 % during the Olympic Games. “The clean air measures were coincidentally boosted by a change in the weather,” explains Dr.

Franz Rohrer, head of the nitrogen oxide chemistry working group at ICG. He focuses on evaluating the results of the Jülich measurements. “Air masses moved around and heavy rain washed much of the particulate matter out of the atmosphere. The environmental protection measures ensured that subsequent new pollution of the air was not as heavy, which led to better air quality for the athletes and for the population.” On the other hand, this combined weather influence makes it difficult to assess in detail how the reduced pollutant emissions affected the atmospheric chemistry.

Enigmatic radicals

In order to understand what happens in the air above the Chinese conurbations, the Jülich scientists now want to simulate the atmospheric conditions in such a way that the weather will not be

able to thwart the measurement results.

“In the SAPHIR atmosphere chamber at Jülich, we can control all of the conditions,” explains Rohrer. “We can set the concentrations of different components in the air and of pollutants to those measured in China and accurately monitor exactly what reactions then occur in the atmosphere with sunlight.”

In particular, the researchers hope to be able to explain the unexpected measurement results they recorded for hydroxyl radicals (OH). These radicals play a key role in the self-cleaning of the atmosphere and are therefore referred to as the “detergent” of the atmosphere.

They are highly reactive compounds formed from a hydrogen atom and an oxygen atom in sunlight. They decompose hydrocarbons, carbon monoxide, nitrogen oxides, and other pollutants.

Jülich is a global pioneer in the precise determination of OH radicals. “Even at high pollution levels, our measurements in Beijing and the Pearl River Delta revealed two-to-three times as many hydroxyl radicals as we had expected,”

reports Dr. Andreas Hofzumahaus, who headed the measurements in China. The scientists had assumed that the radicals would be rapidly consumed due to high levels of pollution. However, it would appear that this “detergent” is recycled faster after reacting with pollutant molecules than was previously believed. Why this is the case is not yet clear. “We have

pinpointed a gap in our knowledge of these photochemical processes. Now we can work in a targeted manner to solve this enigma,” says Hofzumahaus.

Another question that has yet to be answered is why much less ozone is actually formed during the degradation of pollutants above the Chinese megacities than models had previously led us to believe. Normally, for every pollutant molecule degraded, one to two ozone (an important greenhouse gas) molecules are formed. “Our measurements revealed new atmospheric degradation pathways for trace substances,” says Andreas Wahner. In contrast to what was previously assumed, no ozone is formed when trace substances are degraded. “At the moment, we suspect that these degradation processes also occur in other regions on Earth. This could change our understanding of the self-cleaning ability of the atmosphere.” These new insights were published recently in the high- impact journal Science. The Jülich scientists hope to find answers to the remaining questions using experiments in the SAPHIR atmosphere chamber.

Chinese atmosphere in Jülich

The 20-metre-long “laboratory con- tainer” with a diameter of five metres holds around 300 m³ of air surrounded by double-walled Teflon foil. Scientists can mix the air as they choose – for example, they can simulate smog in Beijing Mean tropospheric NO₂ column density (1,015 molec/cm²)

according to measurements using the SCIAMACHY instrument on the ESA satellite ENVISAT for the years 2003 to 2006.