“…The results led to the development of measures to avoid exposure to this pollutant. Furthermore, the European initiatives impacted the participants' knowledge, self-efficacy, and attitudes towards NO 2 pollution; they resulted in changed or adjusted behaviour of the involved citizens towards measures to exposure and contribution to air pollution, led to a higher sense of community, stimulated discussions with policy makers, and influenced political decisions in the involved regions (Francis and Stockwell 2014, Hsu et al 2017, Kloetzer et al 2017, Zannella 2017, Van Brussel and Huyse 2018, Haklay and Eleta 2019. Other projects, such as Luftdaten (https:// luftdaten.info/), HackAir (https://platform.hackair.eu/), and senseBox (https://sensebox.de/) experiment with self-made sensor kits and data platforms to measure particulate matter (PM), a mixture of solid particles and liquids found in the air which are either emitted directly from a source, like a construction site, or are the result of chemical reactions of other pollutants, such as NO 2 .…”