IMK-AAF studies fundamental processes that govern the formation, transformations and sinks of atmospheric aerosols. These processes are of great relevance for climate, cloud and precipitation formation and for human health (IPCC AR5, Chapter 7). Its research is embedded in the Research Program “Atmosphere and Climate” of the Helmholtz-Association, where it contributes to Topic 1, Topic 3 and Topic 4. The institute operates the large Aerosol- and Cloud Simulation Chamber AIDA (Aerosol Interaction and Dynamics in the Atmosphere). Access to this facility is supported via the EU program EUROCHAMP.
Within KIT, IMK-AAF is contributing to the Center for Climate and Environment which addresses societal challenges resulting from changes of the climate and the environment in the context of demographic, economic and technical developments.
The quality of our air is defined by concentrations of specific trace gases and airborne particles as well as their composition. We study aerosol particles and trace gases in urban, rural, and remote locations with the aim to understand the roles of different sources, regional transport, the evolution of the planetary boundary layer, as well as extreme weather events. For this purpose, we combine detailed ground based aerosol characterization with remote sensing methods.
Ice Nucleating Particles
Ice Nucleating Particles (INPs) are a very minor fraction of atmospheric aerosol particles, which are needed to form ice crystals at high temperatures or low ice supersaturation, and by that have important impact on the formation of precipitation and the net radiative effect of cirrus clouds in the Earth’s climate system. The atmospheric abundance and distribution of INPs strongly depends on the temperature as well as the concentration and type of aerosol particles. We are using the aerosol filter based method INSEKT (Ice Nucleation Spectrometer of the Karlsruhe Institute of Technology) and the newly developed PINE (Portable Ice Nucleation Experiment) instrument for INP measurements at about 10 different locations in Europe and in China. We are in particular interested in long-term observations at field sited influences by aerosol from different natural and anthropogenic sources.
Biological Ice Nucleators in the Atmosphere
Living organisms have developed ways of controlling ice nucleation and growth to prevent cell damage caused by freezing of intracellular water. As a result, many microorganisms, such as bacteria, fungi, or plant pollen, have become able to trigger freezing of water at just a few degrees of supercooling, as compared to -40°C degrees required to freeze microscopic droplet of supercooled water homogeneously. Some bacterial and animal proteins are also responsible for inhibiting the ice crystal growth by attaching themselves to the crystalline faces of growing ice. In cooperation with microbiologists from KIT and Aarhus university (Denmark), we study how certain bacteria affect freezing of atmospheric water and how this affects their chance of survival and dissemination pathways.
Atmospheric reactions e.g. heterogeneous ice nucleation, gas deposition, particle oxidation and photosensitization or secondary aerosol and biogenic particle formation dependent on the physical and chemical interactions occurring at interfaces. Understanding the factors that influence atmospheric interactions, particularly on the molecular level, is a major unsolved and pressing problem in our understanding of climate. Our aim is to investigate fundamental processes in the atmosphere on the molecular level using nonlinear optical spectroscopy, mainly second-harmonic generation (SHG) and sum-frequency generation (SFG). SHG and SFG are second order nonlinear optical effects that are only active at surfaces and interfaces where the inversion symmetry is broken.
The smallest long lived nanoparticles in the atmosphere (radius<2 nm) condense from evaporated meteoric material in the mesopause region (h~85 km). There they give rise to an abnormally high radar reflectivity and during summertime at high latitudes act as nuclei for the spectacular noctilucent clouds. We investigate the chemical and physical processes leading to the formation and growth of these ice clouds in the laboratory. To do so, we have developed a unique simulation chamber to expose nanoparticles to the extreme conditions of the mesopause.
In-Situ Aerosol and Cloud Particle Optics
We investigate the interaction of ultraviolet and visible light with atmospheric aerosol and cloud particles in order to (i) measure their shortwave spectral optical properties, (ii) deduce the bioaerosol content, and (iii) study the structural details of ice particles. We develop optical instrumentation that is deployed in aircraft missions, mountain top studies, and cloud chamber experiments.