The first question
30
By its first question, the referring court asks whether Article 4(3) TEU and the second subparagraph of Article 19(1) TEU, read in conjunction with the third paragraph of Article 288 TFEU, and Articles 6 and 7 of Directive 2008/50, must be interpreted as meaning that it is for a national court, hearing an application submitted for that purpose by individuals directly affected by the exceedance of the limit values referred to in Article 13(1) of that directive, to verify whether the sampling points located in a particular zone have been established in accordance with the criteria laid down in paragraph 1(a) of Section B of Annex III to the directive and, if they were not, to take all necessary measures in respect of the competent national authority, such as an order, with a view to ensuring that the sampling points are located in accordance with those criteria.
31
According to settled case-law, under the principle of sincere cooperation laid down in Article 4(3) TEU, it is for the courts of the Member States to ensure legal protection of an individual’s rights under EU law. In addition, the second subparagraph of Article 19(1) TEU requires Member States to provide remedies sufficient to ensure effective legal protection in the fields covered by EU law (judgment of
19 November 2014,
ClientEarth
, C‑404/13, EU:C:2014:2382, paragraph 52
).
32
In addition, the Court has noted on numerous occasions that it is incompatible with the binding effect that Article 288 TFEU ascribes to the directive to exclude, in principle, the possibility of the obligation imposed by that directive being relied on by the persons concerned. That consideration applies particularly in respect of a directive whose objective is to control and reduce atmospheric pollution and which is designed, therefore, to protect public health (judgments of
25 July 2008,
Janecek
, C‑237/07, EU:C:2008:447, paragraph 37
, and of
19 November 2014,
ClientEarth
, C‑404/13, EU:C:2014:2382, paragraph 55
).
33
As the Advocate General pointed out, in essence, in point 53 of her Opinion, the rules laid down in Directive 2008/50 on ambient air quality put into concrete terms the EU’s obligations concerning environmental protection and the protection of public health, which stem, inter alia, from Article 3(3) TEU and Article 191(1) and (2) TFEU, according to which Union policy on the environment is to aim at a high level of protection, taking into account the diversity of situations in the various regions of the European Union, and is to be based, inter alia, on the precautionary principle and on the principle that preventive action should be taken (judgment of
13 July 2017,
Túrkevei Tejtermelő Kft., C‑129/16, EU:C:2017:547
).
34
In particular, where the EU legislature has, by directive, imposed on Member States the obligation to pursue a particular course of action, the effectiveness of such action would be weakened if individuals were prevented from relying on it before their national courts, and if the latter were prevented from taking it into consideration as an element of EU law in deciding whether the national legislature, in exercising the choice open to it as to the form and methods for implementation, has kept within the limits of its discretion set by the directive (judgment of
24 October 1996,
Kraaijeveld and Others
, C‑72/95, EU:C:1996:404, paragraph 56
).
35
Directive 2008/50 lays down detailed rules for the use and location of sampling points to measure air quality in zones and agglomerations established by the Member States in accordance with Article 4 of the directive.
36
Article 6 of Directive 2008/50 lays down different technical methods that Member States are required to use to assess air quality in zones and agglomerations. In accordance with Article 6(2) to (4), in all zones and agglomerations where the level of pollutants referred to in Article 5 of the directive exceeds the upper assessment threshold set out in Section A of Annex II thereto, the ambient air quality is to be assessed using fixed measurements, which may be supplemented by modelling techniques and indicative measurements. Below the upper assessment threshold, a combination of fixed measurements, on the one hand, and modelling techniques and indicative measurements, on the other hand, is permitted. Only when the pollution level does not reach the lower assessment threshold, also set out in Section A of Annex II to Directive 2008/50, can air quality be monitored using only modelling or objective-estimation techniques.
37
Article 7 of Directive 2008/50 concerns the location and minimum number of sampling points. In accordance with paragraph 1 thereof, the location of sampling points for the measurement of sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter (PM10 and PM2,5), lead, benzene and carbon monoxide in ambient air is to be determined in accordance with the criteria set out in Annex III to that directive.
38
Section B of that annex sets out the criteria for the ‘macroscale siting’ of sampling points. It follows from paragraph 1(a) thereof that sampling points directed at the protection of human health must be sited in such a way as to provide data on air quality (i) in the areas within zones and agglomerations where the highest concentrations of the pollutants in question occur to which the population is likely to be directly or indirectly exposed for a period which is significant in relation to the period under consideration for the limit values concerned and (ii) in other areas within the zones and agglomerations which are representative of the exposure of the general population. Paragraph 1(f) of Section B of that annex specifies that sampling points are, where possible, also to be representative of similar locations not in their immediate vicinity.
39
Thus, the provisions of paragraph 1(a) and (f) of Section B of Annex III to Directive 2008/50 require sampling points to provide representative data for locations in a zone or agglomeration characterised by a certain level of pollution.
40
It is apparent from paragraph 1(b) of Section B of Annex III to that directive that sampling points must be sited in such a way as to avoid measuring very small ‘micro-environments’ in their immediate vicinity and that the air sampled must, as far as possible, be representative of the air quality in an area of a certain size. That provision requires that the measurements reflect air quality, at traffic-orientated sites, for a street segment no less than 100 m in length and, at industrial sites, for a plot of at least 250 m × 250 m.
41
In addition, the rules provided for in Annex V to Directive 2008/50, to which Article 7(2) and (3) of that directive refers, make it possible to determine the minimum number of sampling points in a zone or agglomeration and the ratio between the points for measuring background pollution and those for measuring traffic-based pollution.
42
Some of the provisions of Directive 2008/50 referred to in the preceding paragraphs of this judgment contain clear, precise and unconditional obligations, which means that they can be invoked by individuals against the State.
43
This is the case, in particular, with regard to the obligation to establish sampling points in such a way that they provide information on the pollution of the most polluted locations, laid down in the first indent of paragraph 1(a) of Section B of Annex III to Directive 2008/50, and the obligation to establish at least the minimum number of sampling points set out in Annex V to that directive. It is for the national courts to verify whether those obligations have been complied with.
44
It is indeed true that, depending on the local situation in a zone or agglomeration, several sites may meet the criteria laid down in paragraph 1(a) of Section B of Annex III to Directive 2008/50. Therefore, it is the responsibility of the competent national authorities to choose, within the limits of their discretionary powers, the actual location of the sampling points.
45
However, the existence of such discretionary powers does not in any way mean that the decisions taken by those authorities in that connection are exempt from judicial review, in particular in order to verify whether they have exceeded the limits set for the exercise of those powers (see, to that effect, judgments of
24 October 1996,
Kraaijeveld and Others
, C‑72/95, EU:C:1996:404, paragraph 59
, and of
25 July 2008,
Janecek
, C‑237/07, EU:C:2008:447, paragraph 46
).
46
Moreover, despite the absence of rules of EU law on procedures for bringing actions before national courts, and in order to determine the rigour of judicial review of national decisions adopted pursuant to an act of EU law, it is necessary to take into account the purpose of the act and to ensure that its effectiveness is not undermined (see, to that effect, judgments of
18 June 2002,
HI
, C‑92/00, EU:C:2002:379, paragraph 59
, and of
11 December 2014,
Croce Amica One Italia
, C‑440/13, EU:C:2014:2435, paragraph 40
).
47
With regard to Directive 2008/50, the location of sampling points is central to the air quality assessment and improvement system it provides for, in particular where the level of pollution exceeds the upper assessment threshold referred to in Articles 5 and 6 thereof. As noted in paragraph 36 above, in that case, in accordance with Article 6(2) of Directive 2008/50, sampling points are the main instrument for assessing air quality.
48
The measurements obtained with those points enable Member States to ensure, as required by Article 13(1) of Directive 2008/50, that, throughout their zones and agglomerations, the levels of the pollutants identified in that directive do not exceed the limit values laid down in Annex XI thereto. If those limit values are exceeded after the deadline for their application, the Member State concerned is required to draw up, in accordance with Article 23(1) of that directive, an air quality plan which meets certain requirements (see, to that effect, judgments of
25 July 2008,
Janecek
, C‑237/07, EU:C:2008:447, paragraphs 35 and 42
, and of
19 November 2014,
ClientEarth
, C‑404/13, EU:C:2014:2382, paragraphs 25 and 40
).
49
It follows that the very purpose of Directive 2008/50 would be compromised if sampling points located in a given zone or agglomeration were not established in accordance with the criteria laid down therein.
50
That risk may also arise if, within the limits of the discretion conferred on them by Directive 2008/50, the competent national authorities do not seek to ensure that the directive is effective. Thus, in particular if measurements taken at several sites are, in principle, likely to provide information on the most polluted locations for the purpose of the first indent of paragraph 1(a) of Section B of Annex III to that directive, it is the responsibility of the competent national authorities to choose the location of sampling points in such a way as to minimise the risk that incidents in which limit values are exceeded may go unnoticed.
51
In this context, those authorities are required to base their decisions on sound scientific data and, as set out in Section D of Annex III to Directive 2008/50, to prepare comprehensive documentation that includes evidence supporting the choice of the location of all monitoring sites. That documentation must be updated regularly to ensure that the selection criteria remain valid.
52
Therefore, while the choice of the location of sampling points requires technical and complex assessments, the discretion of the competent national authorities is limited by the purpose and objectives pursued by the relevant rules in this respect.
53
Moreover, since individuals are entitled to have a court verify whether national legislation and its application remained within the limits of the margin of discretion allowed in Directive 2008/50 when the location of sampling points was chosen, the court designated for this purpose by national law also has jurisdiction to take all necessary measures in respect of the national authority concerned, such as an order, to ensure that such points are sited in accordance with the criteria laid down in that directive (see, to that effect, judgments of
25 July 2008,
Janecek
, C‑237/07, EU:C:2008:447, paragraphs 38 and 39
, and of
19 November 2014,
ClientEarth
, C‑404/13, EU:C:2014:2382, paragraphs 55, 56 and 58
).
54
In this respect, it is clear from the Court’s case-law that, in the absence of EU rules, it is for the domestic legal system of each Member State to designate the courts and tribunals having jurisdiction and to lay down the detailed procedural rules governing actions for safeguarding rights which individuals derive from EU law, such as Directive 2008/50. However, the detailed rules provided for must not be less favourable than those governing similar domestic situations (principle of equivalence) and must not make it impossible in practice or excessively difficult to exercise rights conferred by EU law (principle of effectiveness) (see, to that effect, judgments of
6 October 2015,
East Sussex County Council
, C‑71/14, EU:C:2015:656, paragraph 52
, and of
22 February 2018,
INEOS Köln
, C‑572/16, EU:C:2018:100, paragraph 42
). As regards the latter principle, it should be recalled that the right to an effective remedy and to a fair trial is enshrined in Article 47 of the Charter of Fundamental Rights of the European Union, which constitutes a reaffirmation of the principle of effective judicial protection (see, to that effect, judgments of
26 July 2017,
Sacko
, C‑348/16, EU:C:2017:591, paragraph 31
, and of
27 September 2017,
Puškár
, C‑73/16, EU:C:2017:725, paragraph 59
).
55
In the present case, it was stated at the hearing before the Court and was not disputed that the national courts with jurisdiction to verify the location of sampling points have, under the relevant rules of Belgian law, a power to issue orders in respect of national authorities. It is therefore for the national court to make use, where appropriate, of that power under the conditions laid down by national law.
56
In view of all the above considerations, the answer to the first question is that Article 4(3) TEU and the second subparagraph of Article 19(1) TEU, read in conjunction with the third paragraph of Article 288 TFEU, and Articles 6 and 7 of Directive 2008/50 must be interpreted as meaning that it is for a national court, hearing an application submitted for that purpose by individuals directly affected by the exceedance of the limit values referred to in Article 13(1) of that directive, to verify whether the sampling points located in a particular zone have been established in accordance with the criteria laid down in paragraph 1(a) of Section B of Annex III to the directive and, if they were not, to take all necessary measures in respect of the competent national authority, such as, if provided for by national law, an order, with a view to ensuring that those sampling points are sited in accordance with those criteria.
The second question
57
By its second question, the referring court asks whether Article 13(1) and Article 23(1) of Directive 2008/50 must be interpreted as meaning that, in order to establish whether a limit value with an averaging period of one calendar year, as laid down in Annex XI to that directive, has been exceeded, it is sufficient that a pollution level higher than that value be measured at a single sampling point or whether it is necessary that the average of the measurements taken at all the sampling points in a particular zone or agglomeration indicate such a pollution level.
58
It has been recalled, in paragraph 48 above, that it is for the Member States to ensure, in accordance with Article 13(1) of Directive 2008/50, that, throughout their zones and agglomerations, the levels of the pollutants referred to in that directive do not exceed the limit values laid down in Annex XI thereto. If those limit values are exceeded after the deadline for their application, the Member State concerned is required to draw up an air quality plan, in accordance with Article 23(1) of that directive.
59
As the Advocate General noted in points 72 to 75 of her Opinion, the wording of Article 13(1) of Directive 2008/50 does not make it possible to answer the second question raised by the referring court. The same applies as regards Article 23(1) of that directive.
60
When a literal interpretation of a provision of EU law does not permit its precise scope to be assessed, it must be interpreted by reference to the general scheme and the purpose of the rules of which it forms part (judgment of
6 June 2018,
Koppers Denmark
, C‑49/17, EU:C:2018:395, paragraph 22
and the case-law cited).
61
It follows from Article 6(1) and the third subparagraph of Article 13(1) of Directive 2008/50 that it is for the Member States to assess compliance with the limit values in accordance with the requirements and criteria set out in Annex III to that directive. As is apparent from paragraph 1 of Section A of that annex, Sections B and C of that annex concern the location of sampling points, but also provide guidance for the implementation of the other air quality assessment methods provided for in Directive 2008/50.
62
In this respect, it was observed, in paragraph 39 above, that the provisions of paragraph 1(a) and (f) of Section B of Annex III to Directive 2008/50 require sampling points to provide representative data for locations in a zone or agglomeration characterised by a certain level of pollution. The system thus designed by the EU legislature seeks to enable the competent authorities not only to know the level of air pollution at the location represented by a sampling point, but also to infer from this the level of pollution at other similar locations. As is apparent from recital 14 of Directive 2008/50, the latter objective is achieved, inter alia, by using modelling techniques.
63
It follows that the determination of the average of the values measured at all sampling points in a zone or agglomeration does not provide a valid indication as to the population’s exposure to pollutants. In particular, such an average does not make it possible to determine the level of exposure of the population in general, since that level must be assessed using sampling points set up specifically for that purpose, in accordance with the second indent of paragraph 1(a) of Section B of Annex III to Directive 2008/50.
64
Article 15 of Directive 2008/50, read in conjunction with Article 2(20) and (23) and Section A of Annex XIV to that directive, confirms that assessment. In accordance with Article 15 of the directive, Member States are to establish an indicator of average exposure to PM2,5. That indicator is not determined on the basis of an average of the pollution level at all sampling points in a zone or agglomeration, but by reference to the values obtained at the points which measure urban background pollution only, which, in accordance with Article 15(4) of the directive, must reflect the general population’s exposure to PM2,5, in accordance with Annex III to Directive 2008/50.
65
In addition, the third subparagraph of Article 23(1) of Directive 2008/50 provides that air quality plans are to incorporate at least the information listed in Section A of Annex XV to that directive. In accordance with paragraph 1 of Section A of Annex XV, air quality plans must identify the place where an exceedance of the limit values has been measured, including the sampling point(s) concerned.
66
In the light of those considerations, it follows from the general scheme of Directive 2008/50 that, for the purposes of the assessment, by Member States, of whether the limit values set out in Annex XI to that directive have been complied with, the level of pollution measured at each individual sampling point is decisive.
67
That interpretation of Article 13(1) and Article 23(1) of Directive 2008/50 is confirmed by the purpose of the directive. As is apparent from recital 2 and Article 1 thereof, that directive aims to protect human health and, to this end, provides for measures to combat emissions of pollutants at source. In accordance with that objective, it is necessary to determine the actual air pollution to which the population or part of it is exposed and to ensure that appropriate measures are taken to combat the sources of such pollution. Consequently, the fact that a limit value has been exceeded at a single sampling point is sufficient to trigger the obligation to draw up an air quality plan, in accordance with Article 23(1) of Directive 2008/50.
68
In view of all the above considerations, the answer to the second question is that Article 13(1) and Article 23(1) of Directive 2008/50 must be interpreted as meaning that, in order to establish whether a limit value with an averaging period of one calendar year, as laid down in Annex XI to that directive, has been exceeded, it is sufficient that a pollution level higher than that value be measured at a single sampling point.