Have you ever laid on the grass as a child looking up at the clouds in the sky wondering where they come from? We think many of us have and this is the research foundation of the Center for Chemistry of Clouds. Clouds are wonderful structures dotted over the skies taking the shapes of childhood fantasies. Clouds have been observed for centuries and for just as long we have tried to explain how they form. Although, we have been studying clouds and how they form for this long, much is still to be learned. Clouds cover more than two-thirds of the sky and influence precipitation patterns, weather, and climate. A prerequisite for cloud formation in the atmosphere is aerosols. Aerosols are liquid or solid particles suspended in the atmosphere. They provide the required interfaces for driving cloud formation and influence cloud lifetime, precipitation patterns and radiative properties.1,2
In the latest assessment report of the climate from the Intergovernmental Panel on Climate Change (IPCC), cloud formation and aerosol-cloud interactions constitute the largest uncertainty in the predictions of radiative forcing, while clouds persist as the least understood component of the climate.3 Incredible progress has been made in understanding cloud physics and aerosol sources, but large knowledge gaps remain in understanding the extensive network of chemical reactions and processes that define what is inside and on the surface of aerosols at any given time and how this drives cloud formation and influences cloud properties. To close some of this knowledge gap, the Center for Chemistry of Clouds seeks to contribute with fundamental, molecular-level insight into atmospheric interfaces and the key processes leading to clouds.
In C3, we hope to unravel the formation, structure, and surface chemistry of atmospheric interfaces leading to clouds. We seek to uncover the molecular level dynamics of the formation and chemical change of aerosols and provide knowledge on how molecules attach to aerosol surfaces. To achieve the ambitious goals in our research foundation, C3 combines five fields within chemistry. The core groups of C3 consist of centre leader Professor Merete Bilde, associate professor Marianne Glasius, associate professor Tobias Weidner, Professor Ove Christiansen, and assistant professor Jonas Elm.
Merete Bilde is an expert in atmospheric and physical chemistry, aerosols, and cloud microphysics. She leads the Atmospherical Physical Chemistry group at Aarhus University. She has conceptualised and built unique research infrastructure for atmospheric research, such as the Aarhus University Research on Aerosol (AURA) atmospheric simulation platform and the AEGOR sea spray generation tank. The C3 will harness the state-of-the-art experimental facilities for atmospheric simulations and studies of cloud formation properties in Merete’s laboratory.
Marianne Glasius leads the research group Analytical Chemistry of the Environment (ACE) at Aarhus University focusing on advanced chemical analysis and atmospheric chemistry. She is a world-renowned researcher in the field of molecular characterization of aerosols for studies of both ambient aerosols and laboratory-generated aerosols. C3 will benefit from Marianne's key expertise and advanced chemical laboratory.
Tobias Weidner leads the research group SurfLab at Aarhus University and he is a leading expert on molecular interactions with surfaces and interfaces. He combines experimental observations with theoretical spectroscopy techniques facilitating the combination of theory and experiments within C3. He has an advanced laser laboratory with seven amplified femtosecond lasers including four ultrafast sum frequency generation spectroscopy setups. His laboratory is unique worldwide and will be crucial in C3 to obtain information about molecular-level interactions and reactions at aerosol interfaces.
Ove Christiansen leads the Molecular Interactions Dynamics and Simulation (MIDAS) research group at Aarhus University. He is an internally recognized researcher in theoretical and computational method development and applications. His work includes novel theories for electronic structure, nuclear quantum dynamics, computational spectroscopy, potential energy surfaces, condensed phase modelling, machine learning, and tensor decomposition. All of the above are essential in C3 for developing and applying accurate theories for understanding different aspects is aerosols, e.g. photochemical dynamics at surfaces.
Jonas Elm leads the Computational Atmospheric Chemistry (CATCH) group at Aarhus University. He is a leading expert in the modelling of atmospheric cluster formation. He models atmospheric processes using state-of-the-art quantum chemical methods. His work with atmospheric cluster formation will be paramount in C3 for modelling local aerosol surface environments providing valuable thermochemical parameters for molecules attaching to the aerosol surface. In addition, he also focuses on chemical reaction kinetics in the gas phase, at aerosol surfaces and in gas-to-particle partitioning, which also comes in handy in C3.
In C3, the integration of complementary experimental facilities and theoretical and computational methods will be used to study cloud formation. The research foundation of C3 is centred on three research focuses.
The first focus is on aerosol formation and properties under different environmental conditions. The temperature and relative humidity at which aerosols are formed largely influence the chemical composition of these. This opens a plethora of new research questions as the chemical composition of aerosols affects their particle water uptake, phase state, surface reactivity, and, thus, cloud formation.
The second focus is on the aerosol phase state, which may impact the cloud formation properties of aerosols tremendously. Secondary organic aerosols exist in many different phases, e.g. as liquids, as amorphous solids or in their glassy states. Recent research even shows the co-existence of several phases within a given particle. This complex particle architecture may modulate water uptake and the effects on clouds - more than an order of magnitude higher cloud droplet formation has been suggested from phase separations in aerosols.
The third focus is on reactions and transformations, which alter aerosols. Processing of aerosols, also called ageing, changes the chemical composition and properties of aerosols over time. Very little is known about the actual changes in the chemical composition and how this affects the surface properties. Processes like reactive uptake of molecules, oxidation of surface species, and photo-induced reactions may alter the surface composition and thereby affect the water uptake. Currently, such processes can not be studied with a single technique
1Seinfeld et al., Improving our fundamental understanding of the role of aerosol−cloud interactions in the climate system. Proceedings of the National Academy of Sciences 2016, 113, 5781-5790
2Masson-Delmotte et al, IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.; Cambridge University Press, 2021
3Abbattet al., New Directions: Fundamentals of atmospheric chemistry: Keeping a three-legged stool balanced. Atmospheric Environment 2014, 84, 390-391
