Opinion of Advocate General Kokott delivered on 28 February 2019.#Lies Craeynest and Others v Brussels Hoofdstedelijk Gewest and Brussels Instituut voor Milieubeheer.#Request for a preliminary ruling from the Nederlandstalige rechtbank van eerste aanleg Brussel.#Reference for a preliminary ruling — Directive 2008/50/EC — Articles 6, 7, 13 and 23 — Annex III — Assessment of air quality — Criteria for determining whether the nitrogen dioxide limit values have been exceeded — Measurements using fixed sampling points — Choice of appropriate sites — Interpretation of the values measured at the sampling points — Obligations of the Member States — Judicial review — Intensity of the review — Power to issue directions.#Case C-723/17.