Fixed sampling points in Europe are situated at different types of stations, defined according to different criteria for macro- and microscale siting.

Briefly, depending on the predominant emission sources, stations are classified as follows:

  • traffic stations: located in close proximity to a single major road;
  • industrial stations: located in close proximity to an industrial area or an industrial source;
  • background stations: where pollution levels are representative of the average exposure of the general population or vegetation.

Depending on the distribution/density of buildings, the area surrounding the station is classified as follows:

  • urban: continuously built-up urban area;
  • suburban: largely built-up urban area;
  • rural: all other areas.

All stations officially reported to the EEA are included in the Europe’s air quality status briefing, independently of their designation for compliance checking, as far as they fulfil the data coverage criteria.

For most of the pollutants, monitoring stations have to fulfil the criterion of reporting more than 75% of valid data out of all the possible data in a year. The 2004 and 2008 Ambient Air Quality Directives set, for compliance purposes, the objective of a minimum data capture of 90% for monitoring stations. However, for assessment purposes, a coverage of 75% allows more stations to be taken into account without a significant increase in monitoring uncertainties. For benzene, benzo(a)pyrene (BaP) and the toxic metals arsenic, cadmium, nickel and lead, it is 13% (according to the air quality objectives for indicative measurements). The exception to the general rule is particulate matter (PM) random fixed measurements, for which the required amount of valid data for the analysis is 13%. Reporting stations not fulfilling the minimum data coverage can be found in the Air Quality e-Reporting: Air quality time series (E1a & E2a data sets).

Measurement data are rounded following the general recommendations under Commission Implementing Decision 2011/850/EU. The number of considered decimals is indicated in the legends for the corresponding maps.

The assessments for PM and SO2 do not account for the fact that Member States can subtract contributions to the measured concentrations from natural sources and winter road sanding or salting under specific circumstances. This possibility is provided by the Ambient Air Quality Directive 2008/50/EC.