This poster presents a large-scale air quality collective measurement (xAire), that followed a citizen science methodology. A broad partnership with 1,650 people from communities around 18 primary schools across Barcelona provided the capacity to obtain unprecedented high-resolution NO2 (nitrogen dioxide) levels. The communities first collectively identified the relevant spots to be measured in their neighborhoods. In a well- coordinated effort, they placed at the same time 800 diffusion tubes in the proximity of 18 primary schools. The tubes were collected exactly 4 weeks after. This way, new and precise information on the air quality in the vicinity of the schools was obtained. These data and their interpretation were presented by the kids to the City Council authorities. The results encourage strengthening collaboration with local communities when exploring environmental health issues.These new data also made possible an updated asthma Health Impact Assessment. It is shown that NO2 levels vary considerably with at some cases very high levels. More than a 1,000 new cases of childhood asthma could be prevented each year by lowering NO2 levels. Also, predictive NO2 models in the city have incorporated this citizen science data as a reliable data source. The data have had the models capacity to improve the spatial high resolution. After the project, families and schools have been able to better assess and to take individual and collective actions to mitigate NO2 conccentration levels around the schools and in each neighborhood. Finally, the results were published in the form of scientific paper, the data were published as Open Data and the protocol reported in a specialized scientific journal (MethodsX), in order to maximize the reproducibility of the study.