Under contract to the Phare Programme
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
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
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,
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
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
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.
For references, please go to http://www.eea.europa.eu/publications/C1I92-9167-123-1/page002.html or scan the QR code.
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