Joost Wessseling works at the Centre for Environmental Quality of the National Institute for Public Health and the Environment. He is an expert on (local) air quality, primarily calculating it, but if needed also measuring it and testing models. Since 2015 he is building his own air quality kits, trying several gas and particle sensors, together with colleagues and interested citizens. Main challenges are in getting the right stable and affordable hardware and be able to make sense of the results.