The measuring stations for NO2 measurement in Germany as defined in the DIRECTIVE 2008/50/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 21 May 2008 on air quality and clean air for Europe and the Neununddreißigste Verordnung zur Durchführung des Bundes-Immissionsschutzgesetzes (Verordnung über Luftqualitätsstandards und Emissionshöchstmengen – 39. BImSchV) Anlage 3 C. Kleinräumige Ortsbestimmung der Probenahmestellen, there are mostly locations that do not meet the requirements. See Holger Douglas: Große Leseraktion: Wie manipulieren Messstationen die Feinstaubmessung in Ihrer Stadt?, Tichys Einblick 23.03.2018.This means that some of the measured values are not valid and cannot be compared with each other.
While the problems were ignored or denied by the federal government and cities (e.g.Wiesbaden), the conference of transport ministers on April 19, 2018 under item 4.2 of the agenda: Air pollution control b) Valid NO2 measurements as a basis for legally compliant air pollution control plans demanded that the validity of measuring point locations be checked in accordance with European requirements. Among other things, it is demanded:
“The Conference of Transport Ministers considers it necessary for the installation of the measuring equipment to be carried out according to a uniform standard throughout Germany and Europe, because comparisons of the measuring results and the necessary legal requirements must be met.
equal treatment of those affected on the ground would otherwise be impossible. The Conference of Transport Ministers suggests that the review should in particular address issues such as
a) the prescribed spatial representativeness of the measurements for a larger area in a city, not only for a small room in the immediate vicinity of the measuring station,
(b) the temporal relevance with regard to the period during which the population is exposed to a relevant exposure,
c) the correct placement of the measuring inlet of the station,
(d) the prescribed avoidance of backwater measurements from crossings,
(e) the prescribed avoidance of measurements below obstacles such as trees.”