Research Overview – Why do we study aerosols & clouds?

Aerosols are airborne particles with sizes typically in the nanometer to micrometer range. They are emitted from both biogenic and anthropogenic sources, and are ubiquitous in the Earth's atmosphere, with concentrations ranging from a handful of particles up to 10´000 particles in the volume equivalent to a dice, depending on the location and season.

Aerosols impact atmospheric chemistry by providing a medium for multiphase- and heterogeneous reactions. They also impact human health, by contributing to air pollution and via particle borne transmission of pathogens and pollutants. Aerosol particles are also key for climate via aerosol-radiation interactions (ARI) and aerosol-cloud interactions (ACI).

ARI denotes the scattering and absorption of solar radiation by aerosol particles, which depends on their chemical composition and size. ACI denotes the impacts of aerosols on cloud formation and microphysical properties by acting as cloud condensation nuclei (CCN) and ice nucleation particles (INPs), forming cloud droplets and ice crystals, respectively. In fact, clouds are the most important factor in regulating the energy balance of the Earth-atmosphere system. Their radiative effects are two-fold: Clouds reflect solar adiation, contributing to a cooling, and absorb and re-emit terrestrial radiation, contributing to a warming. Which of these effects dominates depends on the cloud type and whether it is composed of cloud droplets, ice crystals or a mixture of both. The radiative forcing of ACI has the largest uncertainties of all anthropogenic forcing agents according to reports from the Intergovernmental Panel on Climate Change (IPCC). In particular, a detailed understanding of ice crystal formation and subsequent processes in clouds remains incomplete.

Through laboratory measurements and field observation, our research focusses on understanding the role of aerosols for atmospheric processes, with a special interest in their interactions with clouds. We do this using a combination of different measurement techniques to cover the scales from the microscopic, molecular level to study aerosol formation and composition to the macroscopic level to study particle phase transitions and cloud particle formation.

While tackling important problems related to atmospheric chemistry and physics we also train young researchers on state-of-the art instrumentation used for aerosol and cloud research and associated data analysis techniques.

Research Projects

Ice Crystal Nucleation

Pure ice clouds play a key role in the Earth's climate and energy budget by contributing to a net positive radiative forcing. These clouds form when ice forms on aerosols that cat as ice nucleating particles (INPs). Understanding of the chemical and physical aerosol particle properties that allow them to act as INPs and form ice crystals. We study ice nucleation in the laboratory using advanced instrumentation including continuous flow diffusion chambers.

Hygroscopic properties of aerosols

Aerosol hygroscopicity, i.e., the interaction of aerosol particles with ambient water vapor, is an important property of atmospheric aerosols. Hygroscopicity influences particle water content, which governs e.g. particle reactivity.

Aerosol Phase Behavior & Transitions

The number and types of phases impact particle reactivity and their ability to form clouds. In addition, aerosol phase behavior affects the gas-particle partitioning, i.e., interaction of species in the gas and in the particle phase, which in turn govern particle growth and total particulate mass concentrations.

Aerosol Chemical Composition & Mixing State

Atmospheric aerosol particles often have a complex chemical composition and mixing state. Knowledge of these properties on a single-particle level is critical to develop a fundamental understanding of their ability to act as ice nucleation particles (INPs), as only 1 in about 10⁶ atmospheric particles is an INP.

Department of Chemistry

Research Topics