1. Introduction + 2. Availability of data

AIR POLLUTION BY OZONE IN THE EUROPEAN UNION Exceedance of Ozone Threshold Values in 1996 and Summer 1997 Topic Report 7/1997 part II (Summer 1997) - European Topic Centre on Air Quality By 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

Ozone is a strong photochemical oxidant which may cause serious health problems and damage to materials and crops. Human exposure to elevated levels of ozone concentrations can give rise to decreases in lung function and inflammatory responses. Symptoms observed are coughing, chest pain, difficulty in breathing, headache and eye irritation. Both laboratory and epidemiological data indicate large variations between individuals in response to episodic O₃ exposure, the effects seem to be more pronounced in children than in adults (WHO, 1995). The World Health Organization (WHO) recommends an 8h protection guide value of 120 µg/m³ (WHO, 1996) above which symptoms and damage to respiratory functions can be expected to occur.

In view of the harmful effects of photochemical pollution, the Council adopted in 1992 Directive 92/72/EEC on air pollution by ozone (EC, 1992). The Directive defined threshold values, established procedures for harmonised monitoring, for collecting and exchanging data and for information of the public when exceedances of threshold values occur.

The thresholds set by the Directive are presented in Table 1. As far as data reporting is concerned, two types of reporting can be distinguished according to Article 6 of the Directive:

1. Exceedances of the population information and warning thresholds (date, time, duration and maximum concentration) must be reported to the Commission within one month after occurrence (data is not necessarily validated);
2. Exceedances of all threshold values including some additional statistics (percentiles, maxima) must be provided within 6 months after the end of a calendar year (validated data).

Table 1. Threshold values for ozone concentrations set in Directive 92/72/EEC

According to Article 7 of the Directive, the Commission prepares a report summarising all the information transmitted by the Member States at least once a year. The report for the 1996 calendar year will become available together with this document (De Leeuw and van Zantvoort, 1997)

In this document a first assessment is made of the 1997 summer season, based only on the exceedances of the population information and warning thresholds for ozone, which were transmitted by the Member States after the end of each month.

The report is mainly intended to provide fast feedback to the Member States on their data. It also enables the Member States to compare the levels observed in the past summer season with those observed in other Member States. Note that information presented in this document is not necessarily based on validated monitoring data and hence should be considered preliminary.

According to the Directive, exceedances of the population information and warning thresholds are to be transmitted to the Commission within one month following the observation. On the basis of the experience gained with the ozone data reporting in 1995, the Commission updated the formats to be used and gave additional guidelines to ensure successful transmission of data. The exchange formats have not been annotated in 1997. In this report, the EU definition of data formats are used as reference. If necessary, files were converted at the European Topic Centre on Air Quality (ETC-AQ) for further processing. In this report all data received by the Commission (DGXI) and forwarded to the ETC-AQ not later than 19 September 1997 have been included in the analysis.

14 Member States provided information on the ozone situation this year. 10 Member States transmitted monthly reports on exceedances occurrence from April-August. Ireland, Denmark, Sweden and Finland did not record any exceedance of the 180 µg/m³ threshold this year. No monthly exceedance reports were received from France. It is greatly appreciated by the Commission that Member States were able to transmit data before the formal deadline as set in the Directive. Table 2 presents an overview of observed exceedances per country per month.

Table 2: Overview of observed exceedances per month per country. yes: exceedance of the population information threshold reported, no: no exceedance reported, ?: no reporting received.

Member States were requested to check the information made available to the Commission on ozone monitoring sites implemented in the framework of the Directive. For the interpretation of ozone data it is essential to have information on the direct surroundings of the station since the ozone concentration may be scavenged by locally emitted nitrogen oxides or by enhanced dry deposition which might occur for example under a forest canopy. Member States were requested to classify their stations as street, urban background¹, rural or industrial stations as a first description of the environment of the stations.

Only five countries explicitly reported the number of stations scheduled to be operational during summer 1997 (for 1996, all countries reported this information). It is assumed that the number of stations has not changed since 1996 in countries which did not report the number of stations, with the exception of France and Italy. For these countries an estimate of the number of operational stations has been made on the basis of various information received in 1995 and 1996.

Map 1 presents the location of all ozone monitoring stations (street and urban background taken together as 'urban') assumed to be operational during the 1997 summer season.

1070 ozone monitoring sites are assumed to be operational in the framework of the Directive. From the 1070 ozone monitoring stations, 291 stations are situated in rural areas, 326 stations in urban background environments, 189 are street stations and 264 stations are characterised as industrial station or the monitoring environment was not specified.

Note that due to the fact that only exceedances of thresholds were reported, it is not clear whether stations were operational continuously throughout the summer period. It is possible that ozone concentrations exceeded a threshold at a site but was not reported because the monitoring station was temporarily out of operation.²

In this report exceedances are counted on a daily basis, that is, a day on which a threshold is exceeded at least once, is counted as one exceedance day.

Map 1: Ozone monitoring stations implemented in the framework of Directive 92/72/EEC on air pollution by ozone, scheduled to be operational during 1997.

¹ Urban background: station located in the built-up area of the city but not directly influenced by emission sources such as traffic or industry.
² The annual report (De Leeuw and van Zantvoort, 1997) gives information on the percentage of time stations were operational, most stations score >90%.