The Ozone Directive

The current report was already announced in 1992 when the Council Directive on Air Pollution by Ozone (92/72/EEC; 'the Ozone Directive') was issued. The report analyses the information and data reported to the Commission in the framework of this Directive in 1994, 1995, and 1996. In addition much information, data and models from the UNECE-CLRTAP, EUROTRAC and DGXII programmes were used. The Ozone Directive sets concentration thresholds (Table 1), established a harmonised procedure for monitoring and for exchanging data and it specified requirements to inform and warn the population if necessary. A second and third guiding principle for the current report were the fifth Environment Action Programme (5EAP, Table 2) and the World Health Organization (WHO) air quality guidelines. The 5EAP expresses the aim of non-exceedance of threshold and emission reduction targets for ozone precursors. The WHO guidelines are of importance because the 5EAP states that "WHO values [should] become mandatory at EC level not later than 1998". The WHO guidelines are presented in Table 1.

The basic objective of ozone monitoring under the Directive is to assess the risk of exposure of human beings and vegetation to values in excess of the health and vegetation protection thresholds listed in the upper part of Table 1. According to the Directive, the ozone network is supposed to satisfy the following siting criteria in each Member State.

The 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.

Table 1: Ozone thresholds and air quality guidelines defined the Council Directive on Air Pollution by Ozone and the World Health Organization. 1 ppb ozone » 2 μg.m-3

Threshold value set by Description Criteria based on Value
European Council Directive 92/72/EEC Population information threshold 1 hour average 180 μg.m-3
Population warning threshold 1 hour average 360 μg.m-3
Health protection threshold Fixed 8 hour means (period hours 0:00-8:00, 8:00-16:00, 16:00-24:00, 12:00-20:00) 110 μg.m-3
Vegetation protection threshold 1 hour average 200 μg.m-3
Vegetation protection threshold 24 hour average 65 μg.m-3
WHO Protection of public health maximum of floating 8-h average concentration 120 μg.m-3
Protection of agricultural crops of 5% yield loss AOT40, daylight hours, May - July 3 ppm.h
Protection of natural and semi-natural vegetation AOT40, daylight hours, May - July 3 ppm.h
Protection of forest trees AOT40, daylight hours; April - September 10 ppm.h

Table 2: Current 5EAP emission reduction targets

5EAP Policy Main target
VOC target 30% reduction in 2000 from the 1990 emission levels
NOx target Stabilisation by 1994 and reduction of 30% by 2000 both from 1990 level of emissions

The Member States' data reports for 1994, 1995 and 1996 demonstrate that the Directive has been rather successful in the field of data exchange. Also the information provided to the public has raised public awareness and put the ozone problem higher on the list of political priorities.

However, for assessment purposes the spatial coverage of the network has insufficient density in several countries. Uncovered areas can be noted in both urban and rural monitoring. The 1995 subset of rural/background stations in the EU15 countries is estimated to cover a maximum of 20 - 40% of forests and 30 - 50% of crops. The 1995 subset of urban/street sites covers no more than 12% of all EU15 residents and at most 25% of EU15 city dwellers (city defined as having more than 50,000 inhabitants).

This situation hampers meeting the risk assessment objectives defined in the Directive. Furthermore, the use of exceedances of threshold values as a binary guiding principle (either exceeded or not) for reporting on the status of pollution by tropospheric ozone does not provide much flexibility for making assessments of risks and effects of exposure. A better description of the network in terms of the local environment of the stations and co-location of NOx and O3 measurements, would be helpful.

Background to the tropospheric ozone issue

In the polluted boundary layer ozone pollution is formed from emissions of nitrogen oxides and volatile organic compounds in the presence of sunlight. In the background atmosphere methane and carbon monoxide are of main importance. Exposure to ozone causes health impacts and induces damage to vegetation and ecosystems. Episodes of increased ozone occur every year during periods of anticyclonic circulation, clear skies and high temperatures over many parts of Europe. These episodic concentrations are added to the large scale background concentration which is subject to a variable but mostly upward trend. Much of this trend is explained by the enhanced anthropogenic emissions of nitrogen oxides associated with the increased use of fossil fuels during the industrial period. Implementation of both hydrocarbon and nitrogen oxide control will be necessary to combat ozone both during episodes and 'normal' situations. Oxides of nitrogen are also of importance in the acidification issue and because of documented health effects.

On average for the season, summer ozone levels in Europe show an increasing gradient from the north west to central Europe. The mean diurnal maximum ranges from 60-80 µg.m-3 in the north-western part to 120-140 µg.m-3 in central Europe. There are however many areas and occasions that vary from this average pattern e.g. urban areas, mountainous regions, regions subject to sea breeze phenomena.

Emissions of ozone precursors

Emissions of the ozone precursors grew until the late 1980s but are currently levelling off. Between 1990 and 1994 VOC emissions from the EU15 countries were reduced by 9%. Similar emission reductions of 8% were archived for NOx in the same period. The inventories indicate that the increased number and use of motorised vehicles partially offset the trend of declining emissions in other sectors. Put in the framework of the 5EAP emission reduction targets it is clear that several countries managed to realise a reduction. However, given the current reduction rate, it is unlikely that the remaining required cuts of >20% will be met before 2000.

On average over the EU15, the transport sector accounted for about 45% of total anthropogenic VOC emissions in the beginning of the 1990s. In the case of NOx the largest contribution came from transport with an almost stable share of 64% between 1990 and 1994.

Emissions from vegetation also contribute to the concentrations of hydrocarbons and NOx in the atmosphere and therefore to formation of O3. In the EU15 averaged over the year the contributions are of the order of 20 and 7 percent for VOC and NOx respectively.

Assessment in the framework of the Ozone Directive

The threshold set for the protection of human health is exceeded substantially and in all Member States. More than 90% of the 41 million citizens living within a 10 km radius of an urban/street monitoring station were exposed to an exceedance of the threshold at least once in 1995 whereas more than 80% of these people were exposed to more than 25 days of exceedance. If it is assumed that the ozone climatology observed by the current network can be extrapolated to the full EU15 population, then approximately 330 million people (more than 90%) may be exposed to at least one exceedance per year.

The exceedances reported for the health protection threshold were used to assess the number of additional hospital admissions attributable to ozone exposure if the data reported by the Member States are assumed representative of the full population of all Member States. This extrapolation led to an estimate of about 700 hospital admissions attributable to ozone at concentrations exceeding 110 µg.m-3 as an 8-h average. It is, however, known that exposure to ozone levels below this standard causes significant adverse effects in people engaged in outdoor activities. A conservative estimate of the effects of concentrations in the 60-110 µg.m-3 range indicates that an additional 3000 admissions could be attributed to ozone in total population of 15 EU countries. However, these estimations may reflect an underestimate of the number of hospital admissions. Transient decrements in lung function and increase in hospital admission rates are the ozone health impacts which are relatively well established and quantified. Other health effects, such as respiratory symptoms or short term changes in mortality rates could also result from ozone exposure in Europe but the available information is not sufficient for the quantification of impacts.

In 1994 and 1995 both the 24-h and 1-h average threshold set for the protection of vegetation were exceeded substantially, in all Member States and frequently. In 1995, the full EU15 area of coniferous forest and arable land experienced exceedances of the 24-h mean threshold. In less than one percent of the area of broad-leaved forest exceedances were not observed. The critical level for crops and semi-natural vegetation of 3 ppm.h is exceeded in all Member States except Finland. On average over all EU15 countries only 6% of arable land is not exposed to exceedances of the guideline. In the case of forests Scandinavia, Ireland and the United Kingdom forests are almost fully protected against exceedances. The remaining European forests experience exceedances by a factor 2~3 of the guideline.

The threshold value for providing information to the public is exceeded in most Member States every year, but not or rarely in Finland, Denmark and Ireland. An estimate from the 1996 data revealed that this concerned about 31 million Europeans, which approximates 45% of the urban population living in cities with operational monitoring in that year. The warning threshold is reached incidentally, in particular in the southern countries.

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