What The Arctic is experiencing dramatic changes as a result of anthropogenic climate change: warming more than twice the global average. The overarching aim is to improve our understanding of fundamental aerosol-cloud processes that govern the Arctic climate and its accelerated warming. The goal of this project is to understand what Arctic clouds are made of. To form clouds, water vapour requires a surface to make the transition to liquid droplets or ice crystals. This surface is provided by aerosols; tiny particles suspended in the atmosphere. This project will characterize the chemical and physical properties of both Arctic aerosols and also cloud residuals. Cloud residuals is what remains from cloud particles (droplets and ice crystals) when dried. Why The underlying processes of the observed accelerated changes in the Arctic are not well understood. However, these processes cause changes to the entire global climate system with impacts on weather, ocean circulation, ecosystems and geopolitics. Clouds play a major role in the Arctic system and are one of the main contributors to the overall uncertainties. With the continuing retreat of sea ice and new sea routes/industrial activities, new sources of particles will become more important for the formation of clouds in the Arctic. This work can contribute to improve the predictive capability of climate models by providing much needed observations and improved system/process knowledge for the Arctic, one of the most vulnerable parts of our planet, where climate change manifests most. How Using tools and methodologies from the fields of physics, chemistry and meteorology, I will together with researchers at Stockholm University determine experimentally and in high detail the microphysical and chemical properties of particles that act as nuclei for low-level Arctic clouds. In all most previous work in the Arctic, cloud properties were probed artificially by activating aerosol particles. However, it is possible to study cloud forming properties directly inside clouds, by measuring upon what remains from cloud particles (droplets and ice crystals) when dried. We will group and investigate various aerosol particle types and appoint their likely sources using back-trajectories. SSR The Arctic region is particularly vulnerable to climate change. This fellowship will contribute to improve the predictive capability of climate models. We will produce knowledge, which can inform decision-making in relation to various aspects of climate change and social development in the Arctic. The project outcome is important for understanding past, current and future climate and has as such societal relevance.