Ground-level Ozone
Chemical formula: O3. Regulated under EU Ambient Air Quality Directive 2008/50/EC. Updated WHO global guideline: 2021.
EU limit value
120 µg/m³
8-hour max. Directive 2008/50/EC.
WHO 2021 guideline
100 µg/m³
8-hour max
About Ground-level Ozone
Primary sources: Secondary pollutant formed by sunlight reacting with NOx and VOCs from traffic, industry, solvents.
Health impact: Reduces lung function, triggers asthma, increases respiratory hospitalizations. Highest in summer.
Measurement method: Reference: UV photometry, EN 14625
Air pollutant concentrations in the European Union are reported under two distinct regulatory regimes that European citizens regularly encounter without realising it. The European Union legal limits, codified in the Ambient Air Quality Directive adopted in 2008 and revised in October 2024, set binding annual and daily ceilings that trigger national action plans and Court of Justice infringement procedures. Separately, the World Health Organization 2021 global air quality guidelines reflect the current epidemiological evidence on cardiovascular, respiratory, and cancer outcomes and operate as a non-binding health benchmark. The gap between the two is the policy lever, the revised 2024 directive halves several legal limits and aligns most thresholds closer to the WHO recommendation by January 2030.
The EU regulatory limit for Ground-level Ozone is 1.2× the WHO 2021 health-evidence guideline (120 vs 100µg/m³, both annual means). The revised EU Ambient Air Quality Directive adopted in October 2024 will tighten this gap by 2030.
Top stations measuring Ground-level Ozone
| Station | City | Country | Type | Annual mean |
|---|---|---|---|---|
| Rome-Arenula | Rome | IT | background | 73.4 µg/m³ |
| Nicosia-Centre | Nicosia | CY | traffic | 72 µg/m³ |
| Madrid-Retiro | Madrid | ES | background | 70.8 µg/m³ |
| Athens-Piraeus | Athens | GR | traffic | 70.4 µg/m³ |
| Milan-Pascal | Milan | IT | traffic | 67.5 µg/m³ |
| Naples-Centro | Naples | IT | traffic | 67.5 µg/m³ |
| Zagreb-Centar | Zagreb | HR | background | 65.7 µg/m³ |
| Valletta-Msida | Msida | MT | traffic | 65.5 µg/m³ |
| Barcelona-Eixample | Barcelona | ES | traffic | 65.1 µg/m³ |
| Budapest-Erzsebet ter | Budapest | HU | background | 64.7 µg/m³ |
| Paris-Les Halles | Paris | FR | background | 64.3 µg/m³ |
| Marseille-Cinq Avenues | Marseille | FR | background | 64.3 µg/m³ |
| Ljubljana-Center | Ljubljana | SI | traffic | 62 µg/m³ |
| Munich-Altperlach | Munich | DE | background | 61.8 µg/m³ |
| Hamburg-Sternschanze | Hamburg | DE | background | 61.8 µg/m³ |
| Luxembourg-Centre | Luxembourg City | LU | background | 60.7 µg/m³ |
| Lyon-Centre | Lyon | FR | traffic | 59.2 µg/m³ |
| Vienna-Taborstrasse | Vienna | AT | traffic | 59.1 µg/m³ |
| Bucharest-Cercul Militar | Bucharest | RO | traffic | 58.5 µg/m³ |
| Lisbon-Avenida da Liberdade | Lisbon | PT | traffic | 57.7 µg/m³ |
Source: EEA Air Quality e-Reporting Database (Dataflow E1a). WHO Global Air Quality Guidelines (2021 update). EU Ambient Air Quality Directive 2008/50/EC.
Source: European Environment Agency, Air Quality e-Reporting Database (Dataflow E1a, validated 2024).
Source: World Health Organization Global Air Quality Guidelines, 2021 update.
Every figure on PlainAirQuality is rendered directly from official monitoring-network source data, no number is typed in by an editor. This page draws directly on official monitoring-network source data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.