We are a team of atmospheric scientists interested in chemical and physical processes important in Earth's atmosphere. We are particularly focused on clouds and atmospheric aerosols - tiny airborne particles - and their role in atmospheric chemistry, air pollution, climate change and environmental health.

Utilizing different methods, we study aerosol properties and processes such as phase transitions as well as the formation of cloud droplets and ice crystals on aerosol particles, and implication for microphysical properties. Our work integrates laboratory measurements, field observations and modeling collaborations, to understand atmospheric process across different scales, from the molecular to global scale.

By establishing a fundamental understanding of atmospheric aerosols particles and their key chemical and physical properties, our goal is to understand how they shape cloud formation and properties, air quality and climate.

The gallery below show an insight to different research areas within the group.

Picture of the Aerosol and Cloud Microphysics research group in March 2026.

The formation of ice crystals in the atmosphere is often triggered by aerosol particles that can act as ice nucleation particles (INPs). Only extremely few atmospheric particles are INPs and understanding the chemical and physical properties that allow these particles to form ice remains a topic of ongoing research. Image credit: Kenneth G. Libbrecht

Clouds are the most important factor for Earth´s energy budget. Their radiative impacts depends on the cloud type and microphysical properties. Low clouds, such as the Cumulus cloud shown here, have a net cooling effect for climate. Image credit: Fabian Mahrt

Atmospheric aerosols are tiny particles with sizes typically in the nano- to micrometer size range. That is about 5 times less than the diameter of a typical human hair. Microscope tools provide a powerful way to investigate physical and chemical properties of aerosol particles. Shown here is an optical microscope image of an aerosol sample deposited on a silicon nitrate membrane for further analysis using X-ray microscopy. Image credit: Peter A. Alpert

X-ray microscopy can be used to spatially map the chemical composition of individual particles and explore their mixing state. Shown here is an aerosol sample mounted at the Swiss Light Source, where scanning transmission X-ray microscopy coupled to near-edge absorption fine structure (STXM/NEXAFS) measurements were used to probe spectral maps of the particles. Image credit: Fabian Mahrt

The water content of aerosol particles is a key property for many atmospheric processes. We use different instruments to probe the interaction of aerosols with water vapor. Shown here is a picture of the flow system in our Humidified Tandem Differential Mobility Analyzer (HTDMA) instrument, where dry and humidified air flows are mixed to quantify the water uptake of particles during humidity cycles. Image credit: Fabian Mahrt

The properties of aerosol particles change as they travel through the atmosphere and become involved in cloud processes. Shown here are transmission electron (TEM) images of soot particles, that have (right) and have not been (left) involved in ice crys-tal nucleation in clouds, respectively. Cloud pro-cessing of soot particles leads to a compaction and change in particle morphology. Image credit: Fabian Mahrt

The aerosols phase behavior describes the number and types of phases that forms in individual aerosol particle. It is important for many processes includ-ing particle reactivity, growth and cloud formation ability. Shown here are optical microscopy images of aerosol particles that form one- and two-phase particles, respectively. With our research we aim to explore dependencies of aerosol phase behavior on particle composition and understand dependencies on atmospheric variables such as relative humidity and temperature. Image credit: Fabian Mahrt

In our laboratory, we use state-of-the art aerosol instrumentation to characterize our aerosol samples. Shown here is a scanning particle mobility sizer system that is often used in our experiments to probe the particle size distribution. Image credit: Fabian Mahrt

Group dinner after the peer teaching day 2026.

In our laboratory, we use state-of-the-art aerosol instruments to characterize our aerosol samples. Shown here is a scanning particle mobility sizer system, which is frequently used in our experiments to investigate particle size distribution. Image: Fabian Mahrt

The Aerosol and Cloud Microphysics group is part of the research center Center for Chemistry of Clouds (C3). Read more about C3's research here and contact us for further information.