Atmosphere and Remote Sensing Research
Greenhouse Gases
Biogenic carbon cycle: CO2 is exchanged between the atmosphere and the land surface through biogenic processes such as respiration and photosynthesis. Net, the biosphere acts globally as a sink for man-made emissions. However, biogenic processes are sensitive to climatic changes implying that a precise understanding of processes is needed to understand the contribution of the biosphere under a future climate. We develop such process understanding with a focus on the continental and seasonal scale by combining CO2 satellite measurements, ground-based network data, atmospheric inversions and vegetation models.
Greenhouse gas camera: Strong point sources of CO2 and CH4 contribute significantly to the emission budget of greenhouse gases. Such sources are coal-fired power plants, industrial plants and volcanoes for CO2 as well as oil, gas and coal extraction plants, landfills and wastewater treatment for CH4. To verify emission rates and visualize plumes, we develop and operate a CO2 and CH4 camera based on a grating spectrometer system in the short-wave infrared. The camera can image exhaust plumes with good temporal resolution in the near field of the source from a distance of several kilometers. Given wind information, instantaneous emission rates can be derived.
Ground-based reference measurements: Satellite measurements and atmospheric models for CO2 and CH4 require rigorous validation to ensure that the small gradients of the gases are accurately captured and thus, source and sink patterns are derived correctly. Ground-based measurements provide this validation through highly accurate absorption spectroscopic measurements of sunlight. We operate our Fourier transform spectrometers in national and international networks together with partners worldwide and we develop new techniques for mobile platforms such as ships and road vehicles.
New spectroscopic methods: We develop new spectroscopic methods with the aim of being able to determine the distributions of CO2 and CH4 in the atmosphere more accurately and more densely. This includes the development of radiative transfer models for data evaluation and the construction of instruments. We have developed a spectrometer that measures scattered sunlight in the short-wave infrared spectral range with high resolution and can target any scattering points in the sky and on the Earth's surface. The method is to be used to map local greenhouse gas fields. Initial deployments, for example in Los Angeles with local partners, have been successful.
Volcanoes: The chemical composition of exhaust plumes from volcanoes can provide information about mechanisms inside the volcanoes. We use our absorption spectroscopic methods to measure the concentrations of CO2 as well as sulphur- and halogen-containing substances. Due to the high content of CO2 in the background atmosphere, the measurement of the volcanic CO2 plumes is particularly difficult and requires modern methods. We conduct expeditions to Etna to test the developed methods and to better understand Etna in combination with chemical and geological measurements.
Photochemistry
Ozone in the middle atmosphere: Halogen oxides play a crucial role in ozone chemistry in the upper troposphere and in the stratosphere. The chemical mechanisms and transport processes are understood in principle, but uncertainties exist in the quantitative modeling and in the sensitivity to changing climatic conditions. This is why regular sampling of the middle atmosphere using balloons and airplanes is necessary. For such measurement platforms, we operate and develop spectrometers for the UV and visible spectral ranges that can measure rare gases such as bromine and iodine oxide, which have a catalytic effect on ozone destruction.
Air pollution: Nitrogen oxides play an important role in air pollution in urban areas, especially as they are mainly emitted by combustion engines in traffic. Satellite measurements of these gases need to be validated by ground-based measurements. This is why we operate a UV/visible spectrometer system on our rooftop platform, which is part of the international PANDONIA network and whose data is used for validation purposes.
