The Member States must thus achieve the target values by 2010, save where not achievable through proportionate measures
.With regard to the maximum period during which those values may be exceeded, the number of days per year was kept at 25. Finally, with regard to the long-term objectives below which t
he concentration of ozone in ambient air would no longer represent a risk to human health or the environment, the year 2020 was introduced as the reference year for the studies to be carried out and for a possible review of the Directive
...[+++].