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Ozone (O3) is formed in the atmosphere when heat and light cause chemical reactions between nitrogen oxides and volatile organic compounds (VOCs), including methane, which is also a powerful greenhouse gas (EEA, 2025b). Emissions of these gases occur from anthropogenic sources and, in the case of VOCs, are also biogenic. Ozone and its precursor pollutants are also transported to Europe from other parts of the northern hemisphere and the upper atmosphere. Meteorology plays an important role in air pollution and in interannual variations in pollutant concentrations. This effect is especially significant for ozone, as can be seen in the annual variations.
Map 3. Concentrations of O3 in 2023 and 2024 in relation to the EU target value
In 2023, the highest concentrations were found in the eastern Mediterranean Sea, Italy, the Iberian Peninsula and central Europe (Map 3 and Figure 8).
Table 4. Summary country status for O3 in 2023 and 2024
2023 | 2024 | |
|---|---|---|
Number of reporting Member States/other countries | 27/8 | 27/6(a) |
Number of Member States/other countries with at least one station > EU target value threshold (120µg/m3) | 16/4 | 16/3 |
Number of Member States/other countries with at least one station > EU long-term objective (120µg/m3) | 27/8 | 27/5 |
Number of Member States/other countries with at least one station > WHO short-term guideline level (100µg/m3) | 27/8 | 27/5 |
Number of Member States/other countries with at least one station > WHO peak season guideline level (60µg/m3) | 27/8 | 27/6 |
Notes: (a) In Serbia stations fulfilled the criteria for minimum data coverage only for the WHO peak season calculations.
Figure 7. Percentage of reporting monitoring stations registering O3 concentrations above the EU target value and the WHO guideline levels in 2023 and 2024
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The long-term EU objective for ozone of 120µg/m3 was met at 17% of monitoring stations in 2023 and 22% in 2024.
In addition to data collected from monitoring stations, countries can also use modelling applications to assess compliance with the standards. Based on assessment models, Italy and Poland reported 2023 exceedances of the O3 target value for the protection of health for six and one air quality zones, respectively; and France, Italy and Poland exceedances of the O3 long-term objective for the protection of health in four, 12 and 44 air quality zones, respectively.