This report presents a first evaluation of the reported exceedances of the threshold value for information and warning of the public during summer 1997 (April-August). Information is not necessarily based on validated monitoring data and hence the conclusions drawn should be considered preliminary.

Information on the occurrence of exceedances has been received from all EU Member States for the months April, May, June, July and August with the exception of France. The quality of the exceedance information supplied was good and largely according to EU specifications. Improvements can be made for a number of countries as far as characterization of stations is concerned. Some countries did not supply meta information on stations. 1070 monitoring stations were assumed to be operational this summer.

The threshold for warning of the public (1h > 360 µg/m3) was exceeded at one stations during summer 1997; Lykovrissi (Athens, Greece) on 18 June 1997.

The threshold for information of the public (1h > 180 µg/m3) has been exceeded in all Member States with the exception of Ireland, Denmark, Finland and Sweden.

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 exceedance. On average 3.4 exceedances occurred this year on stations which recorded at least one exceedance. The average length of an episode was 2.7 hours.

The number of stations which reported an exceedance, the occurrence of exceedances at those stations and maximum concentrations during episodes this year were lower than during the 1995 and 1996 summer seasons. This time series is too short to link this decrease to declining pre-cursor emissions. The difference can mainly be attributed to year-to-year weather variability. Especially in northern and western Europe, the weather conditions during the 1997 summer season were on average less favourable for high ozone levels than during the 1995 and 1996 summer seasons. This year, cool and relatively clean Atlantic air masses prevailed on many days during April-July. Although August was a hot and sunny month in large parts of northern and western Europe, relatively clean air masses originating from the Baltic area/western Russia prevailed on many days (N-NE circulation).

A first estimate was made of the percentage of the urban population exposed to at least one exceedance of the population information threshold. Approximately 75 million people live in cities in which one or more ozone stations were operational during the 1997 summer season (38% of the total EU urban population or 21% of the total EU population). 157 cities reported at least one exceedance of the population information threshold value. Approximately 25 million people in these cities were potentially exposed to at least one exceedance. However this estimate should be interpreted with great care. In many cities, only one station is operational and exceedances are unlikely to represent the potential exposure of the complete urban population.


De Leeuw, F., E. van Zantvoort (1997) Exceedance of ozone threshold values in the European Community in 1996. Summary based on the information reported in the framework of the Council Directive 92/72/EEC on air pollution by ozone. European Topic Centre on Air Quality.

EC (1992) Council Directive 92/72/EEC on air pollution by ozone.

Eurostat (1996) GISCO 'Settlements Pan-Europe' Arc-Info database (not dated, received 1996).

Sluyter, R., E. van Zantvoort (1996): Information document concerning air pollution by ozone. Overview of the situation in the European Union during the 1997 summer season (April-August). Report to the Commission by the European Environment Agency Topic Centre on Air Quality.

World Health Organization (1995): Concern for Europe's tomorrow. Health and the environment in the WHO European region. WHO European Centre for Environment and Health.

World Health Organization (1996): Update and Revision of the WHO Air Quality Guidelines for Europe. Classical air pollutants: ozone and other photochemical oxidants. European Centre for Environment and Health, Bilthoven, the Netherlands.


The authors are indebted to Herman Hootsen (RIVM, The Netherlands) for the cartographic contributions and Liesbeth de Waal (RIVM, The Netherlands) for the trajectory calculations. We wish to thank the Royal Dutch Meteorological Institute (KNMI) for providing synoptical charts.

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