Nitrous oxide (N₂O) is increasingly monitored at wastewater treatment plants due to its climate relevance. Beyond regulatory compliance, N₂O is a sensitive indicator of the performance and stability of biological nitrogen removal. If such measurements are mandatory, their full potential should be utilised. When properly interpreted, emission data provide valuable insights into the state and efficiency of biological treatment processes. This presentation shows how off-gas measurements support the understanding and optimisation of biological process operation. The simultaneous measurement of N₂O, CO₂ and O₂ enables a functional interpretation of emission signals: CO₂ reflects biological activity and carbon conversion, while oxygen and oxygen transfer rate (OTR) describe process loading and aeration intensity. N₂O emissions indicate inefficiencies or stress conditions in nitrification and denitrification, allowing emission-critical operating conditions to be identified. In practice, interpreting high-resolution emission and operational data is complex and time-consuming. The key is the identification of distinct process states. Using the ratio of N₂O emissions to OTR as central performance indicator translates complex data into clearly interpretable operational states, enabling rapid process assessment. Overall, this approach transforms emission monitoring from a reporting obligation into a practical tool for process optimisation, supporting reduced N₂O emissions and improved nitrogen removal performance.