Filip Meysman, Sam De Craemer, Wouter Lefebvre, Jordy Vercauteren, Vincent Sluydts, Evi Dons, Hans Hooyberghs, Joris Van den Bossche, Elke Trimpeneers, Frans Fierens

Air pollution remains a key environmental problem in an increasingly urbanized world. To quantify health impacts and support informed policies, the population exposure needs to be accurately monitored. However, the inherent spatial variability of air quality poses a tenacious challenge to this. While concentrations of traffic-related pollutants like nitrogen dioxide (NO2) are known to vary over short distances, official monitoring networks remain inherently sparse, as reference stations are costly to construct and operate. Here we show that citizen science provides an cost-effective way to collect large, spatially distributed datasets that critically complement official monitoring.