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Exceedance of Ozone Threshold Values in 1996 and Summer 1997

Topic Report 7/1997 part I (1996) - European Topic Centre on Air Quality


Frank de Leeuw, Rob Sluyter and Esther van Zantvoort

October 1997

This report was prepared under the supervision of

Gabriel Kielland, Project Manager European Environment Agency

Download the report as PDF File (Approx. 791 Kb)

Table of contents






    2.1 Introduction
    2.2 Data handling



    4.1 Geographic coverage of monitoring stations
    4.2 Annual statistics, 1996
   4.3 Exceedances of thresholds in 1996
        4.3.1 Exceedances of the threshold value for protection of human health
        4.3.2 Exceedances of the threshold values for information and warning of the population
       4.3.3 Exceedances of the daily threshold value for protection of vegetation
        4.3.4 Exceedance of the hourly threshold value for protection of vegetation
    4.4 Summer smog episodes in 1996
    4.5 Data reported for 1989-1996
   4.6 Preliminary survey of exceedances in Italy



ANNEX I. Observed Exceedances and Annual Statistics

ANNEX II. Phenomenology of ozone concentrations


Overview of the situation in the European Union during the 1997 summer season (April-August)




   3.1 Geographical distribution
   3.2 Comparison with previous years


    4.1 Population exposure
    4.2 Territorial exposure





This report is based upon data collected by the European Commission under the Directive 92/72/EEC on air pollution by ozone and presented to the European Council in their meeting of October 1997 as two separate reports, one covering the year 1996, the other covering summer 1997. The Commission requested the European Environment Agency to assist in the reporting obligations. The reports were subsequently produced by the European Topic Centre on Air Quality under contract to the Agency. The separate reports are also available in electronic form on the EEA homepage on the Internet. In this topic report the annual 1996 and summer 1997 reports are reproduced in their original form as presented to the Commission. The differences in available data, the set of threshold values, the number of stations, the location of stations, and the status of the information based on validated 1996 data and non-validated 1997 data, justifies such an approach.

A major asset of this report is the timeliness of its delivery. The assessment of ozone episodes in 1997 was based upon data measured only two months earlier, while the normal production time from field measurements to validated assessment reports is rarely less than eighteen months. This timely reporting has only been possible with the support of the individual contact points within each Member State and the efficient communication established.

The harmful effects of tropospheric ozone on human health and well-being as well as damage to ecosystems is now being recognised as a major concern throughout the Member States of the European Union. The European Community has taken steps to deal with the problem through a number of Directives including the 92/72/EEC Directive on ambient ozone and the 96/62/EEC Directive on ambient air quality assessment and management (the Framework Directive) as well as the decision to develop a Community strategy for the reduction of ozone pollution. The measures necessary to combat pollution remain however a responsibility of each Member State and require political decisions with cost implications and consequences for the development of activities in society. In this political process basic and reliable information on the extent and severity of the problem is essential.

It is the intention of EEA to continue yearly reporting and assessment of the ground level ozone situation in Europe in close co-operation with the European Commission.

Gordon McInnes

Programme Manager


This report summarises the annual information on exceedances of ozone threshold values during 1996 and gives a first evaluation of the observed exceedances of the thresholds during summer 1997 (April-August). According to the Council Directive (92/72/EEC) on air pollution by ozone, Member States have to provide information on ozone levels (statistical parameters, number and duration of exceedances of specified threshold values) on an annual basis before 1 July of the next year. Additionally, exceedances of the threshold values for population information and warning, as set in the Directive, must be reported to the Commission within one month after occurrence. The analysis for the year 1996 presented in this report is based on information made available before 6 August 1997. By then information for the calendar year 1996 had been received from 13 Member States. Data from France was not available. Data from Italy was received at a very late stage and inconsistent with the agreed format and could not be included fully in the report. As weather conditions during August 1997 indicated a high probability of occurrence of exceedances, the preparation of the report on summer 1997 was postponed for two weeks in order to include as far as possible information on the situation in August. All information received not later than 19 September has been included. 14 Member States submitted data; information from France was not available.

From an evaluation of the exceedances and annual statistics, the following conclusions are reached:

  • Ozone monitoring data for the year 1996 have been received from 836 stations within 13 EU Member States; for Summer 1997 14 Member States provided information for a total of 1070 stations.
  • Spatial coverage and documentation on monitoring data quality need improvement. Depending on the local situation, the ozone monitoring stations are characterised as rural, urban, street or other (e.g. industrial). The present subset of rural stations is not representative for the land area of the EU: the subset is estimated to cover only 40-50% of the area. The geographical coverage of the rural stations is rather adequate in North West Europe but in other regions gaps are noted. The subset of urban stations is insufficient to estimate the exposure of the population living in cities with more than 25 000 inhabitants: the urban stations cover about 30% of the urban population, and hence less than 20% of the total population in the EU.
  • The threshold for warning of the public (360 µg/m3 as hourly average concentration) was exceeded in two Member States in 1996: Greece, two stations in Athens on 21 May 1996 (361 and 391 g/m3) and in Italy, at stations in Palermo (14 November 1996, 368 µg/m3) and in Porto Torres (16 December 1996, 371 g/m3). During summer 1997, one exceedance was observed in the Athens conurbation (station Lykovrissi, 383 µg/m3 on 18 June).
  • The threshold value for providing information to the population (180 µg/m3 as hourly average concentration) was exceeded in 1996 in 12 (out of 13 reporting) EU Member States during a limited number of days; Ireland did not report exceedances.

During Summer 1997 this threshold value was exceeded in all Member States with the exception of Ireland, Finland, Denmark and Sweden. In the Member States where exceedances were observed, the number of days on which at least one exceedance was observed ranged from five in Luxembourg to 49 in Italy. 41% of all stations reported one or more exceedances during the 1997 summer season. An initial estimate was made of the percentage of the urban population which was exposed to at least one exceedance of the population information threshold. From all the cities in which at least one monitoring station was operational, 43% (157 cities) reported one or more exceedances. 25 million people (34% of the population in cities with monitors operational) may have been exposed to these exceedances.

  • In 1996, the threshold value set for the protection of human health population (110 µg/m3 as 8-hourly average concentration) was exceeded substantially and in all reporting Member States. The subset of urban stations is assumed to give representative values for the exposure of an urban population of about 65 million people. 86% of this population was exposed to ozone levels exceeding the threshold during at least one day; 6% was exposed to exceedances during more than 50 days.
  • In 1996 the threshold value of daily average concentrations set for the protection of vegetation (180 µg/m3 as hourly average concentration) is exceeded substantially (by up to a factor 3), widely (in all reporting Member States) and frequently (four Member States report exceedances during more than 300 days at one or more of their stations). Exceedances during more than 150 days are estimated for more than 31% of the area for which the subset of rural stations reports representative values.

The threshold value of hourly average concentrations was exceeded largely and widely (reported by 10 out of 13 Member States) on a limited number of days: in 44% of the mapped area exceedances were reported during 1- 5 days.

  • A limited presentation of the percentile values observed in the period 1989-1996 is given for four Member States for which this information was available. Based on the reported data no conclusive answer concerning a trend in percentile values can be given. For the summer season it is noted that in summer 1997 all relevant indicators (the number of stations which reported an exceedance; the number of exceedances at those stations and maximum concentrations this year) were lower than during the 1995 and 1996 summer seasons. This difference can mainly be attributed to year-to-year weather variability.

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