1. Introduction

Under contract to the Phare Programme

PART I
EXCEEDANCE OF EC OZONE THRESHOLD
VALUES IN EUROPE IN 1997.

Summary based on the information reported in the framework of

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

Report to the Commission by the European Environment Agency

European Topic Centre on Air Quality.

Frank de Leeuw

Tim de Paus

October 1998

1. Introduction

Ozone, O₃, is a strong photochemical oxidant which causes serious health problems and damage to materials and ecosystems. Human exposure to elevated levels of ozone concentrations can give rise to inflammatory responses and decreases in lung function. Symptoms observed are cough, chest pain, difficulty in breathing, headache and eye irritation. Both laboratory and epidemiological data indicate large variations between individuals in response to episodic ozone exposure, the effects seem to be more pronounced in children than in adults. Studies indicate that exposure to ozone concentrations in the range 160-360 mg/m³ for a period of 1-8 hours - concentrations often observed in ambient air over Europe - reduces various pulmonary functions.

Ozone exposure of ecosystems and agricultural crops results in visible foliar injury and in reductions in crop yield and seed production. For vegetation a long-term, growing season averaged exposure rather than a episodic exposure is of concern. Adverse effects on vegetation can be noted at relatively low ozone levels. Within the framework of the UN-ECE Convention on Long-Range Transboundary Air Pollution the critical level for ozone is expressed as the accumulated ozone exposure above a threshold of 40 ppb (corresponding with 80 mg/m³). Guideline values of this accumulated ozone exposure of 3000 ppb.h and 10,000 ppb.h are given for crops and forest, respectively. The World Health Organisation in Europe (WHO) came forward with similar guidelines (WHO, 1996b).

It is known that ozone affects materials such as natural and synthetic rubbers, coatings and textiles. However, there are today serious gaps in knowledge on the mechanisms of damage, the attribution of ozone to damage in comparison to other factors and the economic evaluation of such damage. As far as understood there is no "no-effect level" of ozone for material corrosion; it is assumed that dose-response relations for materials are linear or nearly linear under ambient conditions. Recently, synergistic effects of ozone in combination with the acidifying components SO₂ and NO₂ have been reported to lead to increased corrosion on building materials like steel, zinc, copper, aluminium and bronze.

In view of the harmful effects of photochemical pollution in the lower levels of the atmosphere, the Council adopted in 1992 the Directive 92/72/EEC on air pollution by ozone. The Directive came into force in March 1994. It established procedures for harmonised monitoring of ozone concentrations, for exchange of information, for communication with and alerting of the population regarding ozone and to optimise the action needed to reduce ozone formation.

Article 6 of the Directive specifies how the information on monitoring results must be provided by the Member States to the Commission. Regarding the time frame, two main types of reporting can be distinguished. Information on exceedances of the so-called information threshold (article 6 sub 2) and warning threshold (article 6 sub 3) for the ozone concentration is to be provided within one month after occurrence. Information on exceedances of all threshold values given in Article 6 must be provided within six months following the annual reference period (article 6 sub 1). Article 7 of the Directive stipulates that the Commission shall at least once a year evaluate the data collected under the Directive. The present report gives an overview of ozone monitoring results of 1997. Similar overviews of the 1994, 1995 and 1996 annual data have been prepared by the European Topic Centre on Air Quality (de Leeuw et al., 1995; 1996; 1997). Prior to the current report an overview on ozone threshold exceedances during Summer 1997 (April-August) has been presented to the Commission (de Leeuw et al., 1997).

Harmful ozone concentrations are observed over the whole of Europe. Formation of ozone takes place at various space and time scales: the high emission density of reactive precursors in urbanised areas might lead to high ozone levels within the city or at short distances downwind. But ozone precursors may also be transported over distances of hundreds to thousands kilometres, resulting in ozone formation far from the sources. For improving the insight in current ambient ozone levels over Europe, countries outside the European Union have been asked by the European Environment Agency (EEA) to provide information on ozone exceedances in line with the Ozone Directive.

The data reported here do not cover all ozone monitoring stations in the European Union. For inclusion in this report, the data must satisfy certain criteria stipulated in the Directive, concerning inter alia measuring methods, sampling methods, station siting, quality assurance and documentation. Formats on the transfer of data have been defined by the Expert Group on Photochemical Pollution. This group, established by the Commission following Article 7 of the Directive, had several meetings to co-ordinate the work within the Member States and the Commission in the framework of the Directive.

Background information on the current experience and knowledge concerning photochemical air pollution, dealing in particular with the phenomenology of ozone, the scientific understanding as based on experiments and theory, and the insights from modelling studies on the relation between ozone levels and precursor emissions, may be found in Borrell and Van den Hout (1995), Derwent and Van den Hout (1995), Barrett and Berge (1996) and in Tropospheric ozone in the European Union. The consolidated report (Beck et al., 1998) which is currently in preparation following Article 8 of the Directive. In the process of preparing the new "Ozone Daughter Directive", a comprehensive review of almost all aspects concerning ozone pollution is currently prepared by an expert group established by the European Commission. This so-called Position Paper on Ozone will be published in 1999. Some aspects of the ozone phenomenology are briefly discussed in Annex II.

In the very near future a new ozone daughter directive will be put forward by the Commission. In this new proposal long-term objectives and target values for the protection of human health and vegetation will be defined based on the revised guidelines of WHO (WHO, 1996). The target values should be attained, as far as possible, in 2010. In addition, the draft ozone directive proposes alert thresholds for informing sensitive and general information. Whereas for humans an exposure period 8 hours is considered, for the protection of vegetation the relevant period extends over the whole growing season (three months). As a rule of thumb one might say that the targets for protection of vegetation will be more difficult to meet than the human health related targets.

While the revised WHO guidelines are also relevant in the context of preparing the new daughter directive for ozone an attempt has been made to evaluate the ozone data submitted under the framework of the current directive against these guideline levels, see section 4.5.