4. The current Ozone Directive and other relevant legislation

4.1 Council Directive 92/72/EEC on air pollution by ozone

Currently, European Union countries have to comply with Council Directive on air pollution by ozone (92/72/EEC) which was adopted in September 1992. This Directive defines several threshold levels and it establishes a harmonised procedure for monitoring and exchanging data. It also arranges to provide the public with information when warning and information threshold levels are exceeded. The threshold levels are equal to the WHO guidelines valid in 1992. Table 4 presents the current threshold values.

Table 4: Threshold levels set by the Council Directive on air pollution by ozone

Threshold value set by Description Criteria based on Value μg.m-3
European Council Directive 92/72/EEC Population information threshold 1 hour average concentration 180
Population warning threshold 1 hour average concentration 360
Health protection threshold Fixed 8 hour mean concentrations (period hours 0:00-8:00, 8:00-16:00, 16:00-24:00, 12:00-20:00) 110
Vegetation protection threshold 1 hour average concentration 200
Vegetation protection threshold 24 hour average concentration 65

According to the Directive, Member States have to forward to the Commission:

  • maximum, median and 98-percentile values of 1-h and 8-h mean concentrations;
  • number, date and duration of periods during which the threshold levels quoted in Table 4 were exceeded;
  • maximum concentration recorded during an episode of exceedance.

Member States should base their information on validated continuous measurements. The data should be transmitted to the Commission within 6 months after the end of each calendar year. However, exceedances of the information and warning levels should be reported on a monthly basis. Furthermore, information on siting and measurement techniques is also supposed to be supplied. In turn the Commission prepares, with the assistance of the European Environment Agency and its Topic Centre on Air Quality (ETC/AQ), an annual and a 'summer' report summarising all statistics and exceedances provided by the Member States (e.g. de Leeuw et al. 1995; De Leeuw and van Zantvoort, 1996, 1997; Sluyter and van Zantvoort, 1996).

4.1.1 Monitoring requirements under the Ozone Directive

The Directive states that complete knowledge of ozone pollution is required in all Member States and that it is necessary to use measurement stations to provide data on ambient ozone. In each Member State the ozone network is supposed to satisfy two siting criteria:

  1. Stations should be located at geographically and climatologically representative sites where:
  • the risk of approaching or exceeding threshold values is highest;
  • it is likely that either the population or vegetation is exposed.
  1. Additional stations should be available in order to:
  • contribute towards the identification and description of the formation and transport of ozone and its precursors;
  • monitor changes in ozone concentrations in areas affected by background pollution.

At this second category of stations measurements of NOx are mandatory and those of VOCs are recommended. Observations of NOx and VOC should be carried out in order to provide information on ozone formation, or monitor transboundary fluxes of VOCs and to make it possible to identify links between the different pollutants. Member States are not obliged to inform the Commission on the results of these additional pollutant measurements. No quantitative requirements on network density are provided by the current Directive.

It may be interesting to note that similar station siting criteria, in particular related to urban monitoring, were already formulated in the nineteenth century (Fodor, 1881).

4.1.2 Assessment of exposures, risks and effects versus the network description

The basic objective of ozone monitoring under the Directive is to assess:

  • the individual risk of exposure of human beings to values in excess of the health protection thresholds;
  • the exposure of vegetation (forests, natural ecosystems, crops, horticulture) to the thresholds listed in Table 4.

The Directive does not describe methods to assess exposures, risks or effects of those at risk. For any assessment, a detailed network and site description is an important background for evaluating the representativeness of the ozone networks and for correctly judging the air quality information from these networks. In its communication to Member States on the transfer of the 1996 data, the Commission requested to use a site classification in rural, urban and street stations and a more detailed description of the immediate environment of a monitoring station.

4.2 Other relevant legislation

4.2.1 Council Decision 97/101/EC - Exchange of Information (EoI)

Council Decision on Exchange of Information (97/101/EC) emphasises that data collection, exchange and harmonisation of monitoring information is expected to support the Commission and individual Member States in combating air pollution. More specifically the EoI deals with reporting requirements, the so-called reciprocal exchange, of air pollution data. There are no monitoring requirements set in the EoI Decision. The reciprocal exchange of information currently covers 37 pollutants, among which ozone and its precursors, and includes a classification scheme for stations based on type and the zone where the station is located. The observation stations covered are those under the current air quality Directives, background stations and sites operational under the previous Exchange of Information Decision (82/459). The Commission is responsible for the implementation of the reciprocal exchange. However, the Commission calls upon the European Environment Agency for the practical implementation of the EoI. Member States are to submit data of a particular year by October of the subsequent year. The data sets reported on ozone consist of the mean, median, 98th percentile, and maximum both for 1-h and 8-h averages. For some stations a selection of these statistics is reported. Furthermore, continuous 1-h average concentrations are deposited into the data archive. Until 1995 the data were stored in a Commission-funded database and were made available to the Member States via the Air Pollution Information System (APIS) PC-application. Currently, the EoI data are stored in the


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Filed under: tropospheric ozone
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