First of all I would like to congratulate the author for this very interesting and very complete work on the real use of sensor system in an epidemiologic study. The use of the uncertainty as a marker for reliability is a very interesting choice. However, I would like to emphasize that the European Directive DQO uses a specific value usually taken as the limit value set by the Directive itself. Nevertheless, the work presented in this paper ha been carried out with great care resulting in a very nice publication. You can find below some comments I had on some specific point:

• Table 2: in the comparison with outdoor AQMS, how did you defined the 6km limit ?
• Line 272-273: the REU needs to be calculated at a given value, usually the limit value also set in the Directive. You do not mentionned those value here, will you use a specific one ?
• Line 281: why did you mentioned both directive as the 2024 will overcome the 2008 ?
• Figure 3: this kind of figure is not easy to read. I do understand that the main idea is to show a general trend but I'm a bit overwhelmed by so many information.
• Figure 3: which indicative measurement DQO did you select 2008 or 2024 ?
• Figure 6: I would advise the author to change the color scheme, currently indoor (pink) and outdoor (dark pink) to get a more distinguishable colors.