Citizen science should be promoted and used to raise awareness. It is important to stress though that the quality of the data from those low cost sensors is in general far from sufficient to be used for drawing conclusion on the actual air quality situation and form basis for control measures. This links to the need for harmonization of practices for local measures, such as retrofit approaches and low emission zones. It is recommended to the parties to review and share their success story in the cities. It is not only a problem of scale but also of balance between sectors and other policies. Therefore local actions need to be city specific.