The map shows the proximity of measured O3 concentrations to the target value set in the European Union's Air Quality Directive. At sites marked with dark orange and red dots, the daily maximum 8-hour mean O3 concentration exceeds the 120 μg/m3 threshold on more than 25 days per year (the policy target is set at max. 25 days of exceedance per year, averaged over 3 years).
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