The presentation covers the importance of radon as a tracer and how we are measuring it at ENA station (Graciosa Island, Azores) and Mace Head station (Ireland). We also present the method on how to classify air masses with radon and application on N₂O at three example main baseline sites and how NuClim will contribute to the network of measurement stations. About the speaker:Craig Lils is a Graduate Scientist at NPL working on Greenhouse Gas Metrology to improve our understanding of uncertainty in emissions estimates. He did a MSc in Natural Sciences at the University of Exeter which equipped him with experience in climate science and data analytics.