Sensor data regarding traffic and air quality was gathered as part of the EU Horizon2020 COMPAIR project in Europe. The pilot cities/regions are Berlin, Athens, Sofia, Plovdiv, and Flanders.During the project, the data was published through an OGC SensorThings API. To persist after the project, the air quality related are available as CSV exports, with the retention of the API's structure (Location, Thing, Datastream, Sensor, ObservedProperty, and Observation). Observations about air quality contain sensor readings regarding nitrodioxide (NO2), black carbon (BC), particulate matter (PM1.0, PM2.5 and PM10), humidity and temperature. The NO2 observations are calibrated data streams.The traffic observations remain available through the API of the Telraam platform.