Within the theme of air quality and atmospheric composition, we aim to advance the fundamental understanding of atmospheric composition and air quality by integrating cutting-edge modelling and observational techniques across scales. Our research leverages a diverse array of remote sensing and in-situ observations, spanning satellite, airborne, and ground-based measurements (Loobos, Veenkampen, mobile) of ozone, nitrogen oxides, volatile organic compounds, ammonia, carbon dioxide, and particulate matter to improve understanding and refine models. Our work embraces the complexity of atmospheric processes, addressing both fundamental scientific questions and pressing societal challenges, including air pollution, emissions verification, and excess nitrogen deposition.