Are you from Liège? Want to take part in a great project to measure certain pollutants when you walk? 
by bike 
or by car 
in the center? By taking on board a sensor and participating in Inter Environnement Wallonie’s citizen study on air quality (in which we are collaborating), you will be able to help analyze 
exposure of road users to organic carbon -black carbon- and (ultra)fine particles. Measurements will be organized the week of March 21 and the week of April 19.
https://www.iew.be/oufti-les-liegeois-ne-manquent-pas-dair-le-projet-particulair-prend-son-envol-participez/