The atmosphere interacts closely with the rest of the Earth system including the biosphere, hydrosphere, cryosphere, and lithosphere as well as with urban areas and societies on time scales from seconds to millennia. Changes in one of these components are directly or indirectly communicated to other components via intricately-linked processes and feedbacks. In recent years, scientific research has highlighted the tight connections of reactive gases, greenhouse gases (GHGs) and atmospheric aerosol particles via physical, chemical and biological processes occurring in the atmosphere and biosphere and at their interface. The potential of the biospheric processes to affect radiative forcing has also received significant research attention. The basis for our success has been a deep understanding of multi-scale processes, which requires combining multi-disciplinary theoretical work, empirical measurements, equipment development and multi-scale modelling. This process-level understanding is the backbone of our two main science focus areas at the moment: the COBACC (COntinental Biosphere-Aerosol-Cloud-Climate) feedback hypothesis related to climate change, and a comprehensive multi-pollutant approach to air quality. The COBACC feedback can be considered a broad framework that connects human activities, the continental biosphere, and changing climate conditions.