From nitrous oxide fertiliser to ammonia clouds, researchers at Karlsruhe Institute of Technology tackle the environmental impact of emissions from the agriculture industry.

Together with carbon dioxide and methane, nitrous oxide is among the most important greenhouse gases: It is about 300 times more hazardous to the climate than carbon dioxide. In Germany, the main source of nitrous oxide emissions is agriculture and its extensive use of nitrogen fertilisers.

Potential consequences on food production and climate change will be studied by a new research group of Karlsruhe Institute of Technology (KIT) under the programme “Make Our Planet Great Again – German Research Initiative.” The German-French programme is aimed at strengthening climate research after the Paris Agreement.

“scientists have long been working on quantifying the source strength of agricultural systems for N2O”

Within the framework of the joint funding programme based on the initiative “Make Our Planet Great Again” of the French President, excellent researchers from abroad are invited to work on projects of their choice that support the Paris climate objectives at a French or German institution. The new group at KIT will be headed by Dr Clemens Scheer, who comes from Queensland University of Technology in Brisbane, Australia.

No laughing matter

Dinitrogen monoxide (N2O), also known as nitrous oxide or laughing gas, has a global warming effect, damages the ozone layer, and is formed microbiologically in (over-fertilised) soils, water or sewage treatment facilities as well as by combustion processes. At the Atmospheric Environmental Research Division of KIT’s Institute of Meteorology and Climate Research (IMK-IFU), scientists have long been working on quantifying the source strength of agricultural systems for N2O. Among others, they found that emissions can be reduced, if farmers would adapt the use of fertilisers better to plant growth and if catch crops would be grown.

These – so far regional – studies will now be extended by the global component and the aspect of food production. “We will focus on the question of how more food can be produced at lower environmental costs in order to meet the increasing demand of a growing world population,” says Professor Klaus Butterbach-Bahl of IMK-IFU, who also investigates N2O emissions from livestock farming in steppes and savannas. In parallel, it is planned to establish a global network of researchers studying these questions in order to develop joint standards for measurement and modelling.

Research of Dr Clemens Scheer concentrates on the impact of land use and agriculture on the exchange of environmentally effective gases between the soil, plants, and atmosphere. “The programme offers ideal prerequisites to push my research interests in agriculture and climate change,” Scheer explains. “I am very happy about the opportunity to work at KIT in the next four years: it offers state-of-the-art technology and equipment as well as a stimulating academic environment.”

German Academic Exchange Service

The panel of experts of the German Academic Exchange Service (DAAD) selected Clemens Scheer as one of 13 renowned international researchers to head projects in Germany that support the Paris climate objectives. They are part of the German-French funding programme agreed upon by both governments after the Paris Climate Agreement. The German Academic Exchange Service (DAAD) and the Federal Ministry of Education and Research (BMBF) fund the projects with a total of EUR 15 million. Altogether, more than 700 researchers from all five continents and about 70 countries applied. Clemens Scheer’s group at KIT will be granted funding in the amount of EUR 775,000 by DAAD and BMBF.

Ammonia from agriculture

Outside of their European project, the Climate Researchers of KIT have also been solving the puzzle of a huge aerosol layer in the atmosphere, with a view to results helping to improve climate models.

With measurement flights during the Asian monsoon, satellite observations, and laboratory analyses, researchers solved the puzzle of the Asian tropopause aerosol layer.

The Asian tropopause aerosol layer (ATAL) is located at 12 – 18km height above the Middle East and Asia. This accumulation of aerosols in the Asian monsoon was discovered first in 2011. Its composition and effect, however, have been unknown so far. A European consortium of scientists has now found at this layer consists of crystalline ammonium nitrate. In the AIDA cloud chamber, climate researchers of Karlsruhe Institute of Technology (KIT) demonstrated how this substance is formed in the upper troposphere.

Using a smart combination of remote sensing, in situ measurements, meteorological model calculations, specific laboratory measurements, and detailed numerical simulations, the team studied the distribution and composition of aerosols in the ATAL. Aerosols are smallest suspended particles from a variety of natural and anthropogenic sources. In the atmosphere, aerosols act as condensation nuclei to which gaseous water vapour attaches and, thus, forms cloud droplets. For the first time, a research aircraft flew through the upper levels of the Asian monsoon to study key processes of global importance. The different methods and instruments complemented each other to verify the measured results. Scientists from KIT, Forschungszentrum Jülich (FZJ), Johannes Gutenberg

University and Max Planck Institute for Chemistry, both in Mainz, Alfred Wegener Institute, the University of Wuppertal, Laboratoire de Métérologie Dynamique, Paris, and the Istituto di Scienze dell’Atmosfera e del Clima, Rome, took part.

“Surprisingly, we detected crystalline ammonium nitrate as a main constituent in large parts of the ATAL,” says Dr Michael Höpfner from thAtmospheric Trace Gases and Remote Sensing Division of KIT’s Institute of Meteorology and Climate Research (IMK-ASF). The unexpected results measured, among others, by the GLORIA instrument of KIT and Forschungszentrum Jülich were then confirmed by climate researchers at KIT’s AIDA cloud chamber: “Our experiments revealed that, contrary to the prevailing opinion, liquid ammonium nitrate droplets crystallize to solid particles at minus 50 degrees in the presence of small, mainly sulphur-containing pollutions. These solid particles continue to exist even under temperature and humidity conditions of the upper troposphere,” says Dr Robert Wagner from the Atmospheric Aerosol Research Division of KIT’s Institute of Meteorology and Climate Research. With satellite observations, the researchers indeed found large amounts of ammonium nitrate aerosols above Asia. These observations reach back into the year 1997 when the ATAL was not yet supposed to exist.

“With this, we have solved the long-standing puzzle of the composition of ATAL,” says Michael Höpfner. So far, it has been considered highly improbable that this aerosol exists at such high altitudes, because the precursory ammonia gas is washed out of the atmosphere very quickly by rain. “But we detected unparalleled ammonia concentrations during the Asian monsoon: the values are up to fifty times higher than in previous measurements,” Höpfner adds. This ammonium mainly originates from agriculture, in particular from lifestock farming and fertilization. The highest ammonia emissions are currently found in

Asia. During the monsoon, polluted air masses are transported from the land surface to heights of up to 18 km. Here, ammonia reacts to ammonium nitrate, an aerosol that influences both the formation and properties of clouds.

“It is now for the first time that our data prove that ammonium nitrate aerosols are omnipresent in the upper troposphere during the Asian monsoon,” Höpfner says. These results are relevant in particular to the interactions of clouds and aerosols, which represent one of the biggest uncertainties in climate modeling. Moreover, the findings prove that ammonia emitted on the ground has a big influence on the processes in the upper troposphere and potentially on the Asian climate.

“it is now for the first time that our data prove that ammonium nitrate aerosols are omnipresent in the upper troposphere during the Asian monsoon”

Tracking down ammonia

The aircraft campaign was part of the StratoClim project in which 37 scientific organizations from eleven European countries, the USA, Bangladesh, India, and Nepal collaborate under the direction of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research. The high-altitude aircraft M55-Geophysika carried 25 specially developed instruments to heights above 20 km, about twice the height usually reached by airplanes. A major instrument on board of Geophysika was the infrared spectrometer GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) measuring height distribution of a variety of trace gases along the flight path. Measurements during the flights mainly concentrated on ammonia, as it is largely involved in the formation of aerosol particles. GLORIA presently is the only instrument that can measure ammonia at these heights.

Based on the data measured by the satellite instrument MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) of KIT’s IMK-ASF for height distribution of more than 30 trace gases between Image © Rutherford-Appleton Laboratories, UK 2002 and 2012, the scientists for the first time acquired the global distribution of ammonia and ammonium nitrate at the same time. For their studies, they also used the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) facility on KIT’s Campus North. It is the only facility worldwide, where aerosol and climate processes can be studied under atmospheric conditions. In the facility, all temperature and pressure conditions in the lower and middle atmosphere can be simulated.