The Directive was proposed by the European Commission in mid-1991 (ENDS Report 198, pp 42-43). Unlike three earlier Directives on smoke, sulphur dioxide, lead and nitrogen dioxide, it does not set binding air quality standards. Instead, Member States will have to establish ozone monitoring networks and ensure that the public are informed when two out of four ozone threshold concentrations are exceeded.
The reasons why no air quality standards have been set is that existing international guidelines on the protection of health and vegetation from damage by ozone are breached with great regularity across the Community, and emissions of the primary or precursor pollutants which contribute to the formation of ozone when exposed to sunlight - volatile organic compounds (VOCs) and nitrogen oxides - will not be reduced to any significant extent until the end of the century. Better information is also needed on the formation and transboundary transport of ozone and its precursors, especially in southern EC countries where the problem is most severe.
The Directive obliges Member States to establish a network of ozone monitoring stations in accordance with criteria specified in an annex. These are little changed from the Commission's original proposal.
In the UK, where only 17 ozone monitoring stations were operated until recently, further instruments are being added as the urban air quality monitoring network is expanded. The need for additional monitoring stations will have to be determined in the light of "indicative measurement programmes" required by the Directive in areas where humans or vegetation are likely to be exposed to ozone above the four thresholds prescribed by the legislation, but where no information on ozone levels is available.
Ozone measurements will have to be carried out by means of a reference method, or any other method which is shown to give equivalent results. The reference technique originally proposed by the Commission was the chemiluminescence method, but in the final text this has been altered to UV absorption, which is favoured by the UK.
The Directive includes four ozone thresholds:
Action to inform the public will have to be taken when the latter two thresholds are exceeded. Specified information will have to be disseminated "on a sufficiently large scale as soon as possible to enable the population concerned to take all appropriate preventive protective action." The information to be imparted includes the population and area affected, a forecast of whether ozone levels are likely to increase, remain stable or decrease, and health precautions.
A system of ozone warnings is already operated in the UK. However, warnings to sensitive groups have until now been issued when ozone levels exceeded 200µg/m3, while general warnings to people to avoid unnecessary exercise would not be sounded until ozone levels reached 400µg/m3. Both values are higher than the two thresholds set in the Directive. Exceedances of the lower, population information threshold are likely to be common in the UK during photochemically active years, as in 1989 (ENDS Report 198, p 8).
Exceedances of all four threshold values, as well as other details of the measurements made by the national monitoring networks, will be reportable to the Commission from the beginning of 1995.
The Commission is obliged to evaluate the information collected at least once a year and to submit its findings to Member States. A series of consultations will also be organised by the Commission to consider trends in ozone levels, transboundary ozone pollution episodes, and national programmes to curb ozone pollution.
The original draft contained a proposal that Brussels should put forward a further legislative proposal on ozone pollution by July 1997, and that this should contain air quality standards for the gas.
However, the final text leaves the matter more open. It says that the Commission should prepare an evaluation of photochemical pollution in the Community by February 1998, and accompany this report with "any proposals the Commission deems appropriate on the control of air pollution by ozone and, if necessary, for reducing emissions of ozone precursors."
In fact, some Community laws on ozone precursors have already been adopted, and others are likely to follow by 1998. Already adopted are Directives on emissions of VOCs and NOx from vehicles and of NOx from large combustion plant. A recent proposal to curb emissions of VOCs from the petrol storage and distribution chain (ENDS Report 212, pp 30-31 ) is due to be followed shortly by another on VOC emissions from vehicle fuelling operations. And a Directive on solvent emissions from several industrial sectors is likely to be proposed next year. However, these are unlikely to be the end of the story.
Meanwhile, Member States must bring the ozone Directive into force by 21 February 1994.