Humans modify the Earth’s surface through agriculture, forest management, urbanization, and industrial activities. This land-use change alters the emissions of different chemical compounds from the surface to the atmosphere, thus being an important driver for change in atmospheric composition. The composition of the atmospheric air, on the other hand, is critical for both human health as well as the Earth’s radiative balance and climate. The proposed project aims at filling critical gaps in the scientific knowledge required for quantifying the impacts of land-use on concentrations of atmospheric particulate matter – which is a key component in determining air quality and as well as the energy budget of the Earth. Specifically, we will focus on studying the processes through which emissions of organic and nitrogen-containing compounds from forests and agricultural land-use influence the concentrations of ultrafine (<100 nm) aerosol particles. To achieve this, we will combine high-precision laboratory experiments conducted in the CLOUD facility at CERN with the development and application of state-of-the-art air quality and climate models based on the experimental data. This approach guarantees the interaction between the forefront basic research and the development of modeling tools that are directly applicable for policy support. The results of the project will provide input for designing land-use policies for optimal air quality, climate, societal and economic impacts.