Our central goal is to expand our understanding of tropospheric processes and accurately model the atmospheric composition. For that we constantly probe for unobservable processes to explain the chemical state of the atmosphere. Our research focuses on multiphase processes involving tropospheric oxidants and pollutants in the gas and condensed phases. We investigate to which extent observations are predictable and informative about the internal states of the atmosphere. This knowledge allows us to reliably predict air quality and optimize the emissions of pollutants. Furthermore, we explore the interactions between weather and atmospheric composition and how the latter mediates the coupling between the biosphere and the climate system.