The regulated seven
The EU Ambient Air Quality Directive 2008/50/EC, supplemented by the 4th Daughter Directive 2004/107/EC, regulates seven outdoor air pollutants in the ambient (outdoor) environment.
1. PM2.5, Fine Particulate Matter
Particles up to 2.5 µm in aerodynamic diameter. Sources: combustion (vehicles, residential heating, industry) and secondary formation. EU annual limit 25 µg/m³ (falling to 10 by 2030), WHO 2021 guideline 5 µg/m³. PM2.5 is the single highest-burden pollutant in Europe, attributable to about 238,000 premature deaths per year across the EU-27 (EEA Burden of Disease, 2022, modeled attributable estimates, not counted deaths).
2. PM10, Coarse Particulate Matter
Particles up to 10 µm. Sources: mechanical processes, road wear, construction, agriculture, wind-blown dust. EU annual limit 40 µg/m³, WHO 2021 guideline 15 µg/m³.
3. NO2, Nitrogen Dioxide
Primarily emitted from combustion at high temperatures, especially diesel vehicles. EU annual limit 40 µg/m³, WHO 2021 guideline 10 µg/m³. Inflames the airways; causally linked to new-onset asthma in children. Traffic monitoring stations across most European capitals exceeded the WHO guideline in 2024.
4. O3, Ground-level Ozone
A secondary pollutant formed in sunlight from NOx + VOC chemistry. EU 8-hour target 120 µg/m³, WHO 2021 guideline 100 µg/m³ (peak season 60 µg/m³). Highest in Mediterranean summers. Reduces lung function; triggers asthma exacerbations.
5. SO2, Sulfur Dioxide
From coal and high-sulfur fuel combustion. Largely controlled in the EU since the 1990s (Large Combustion Plant Directive). Daily limit 125 µg/m³ - rarely approached. Continues to matter in industrial regions and on shipping routes.
6. CO, Carbon Monoxide
From incomplete combustion. 8-hour limit 10 mg/m³ (note: mg, not µg, because concentrations are higher). Binds to hemoglobin, reducing oxygen transport. Indoor CO from faulty boilers is more dangerous than ambient outdoor CO.
7. Benzene (C6H6)
From vehicle exhaust, petrol stations, industrial solvents. EU annual limit 5 µg/m³. WHO Group 1 carcinogen, no safe exposure threshold for leukemia risk. The operational guidance is "reduce to lowest practicable level."
Also regulated
The 4th Daughter Directive 2004/107/EC adds target values for arsenic, cadmium, mercury, nickel, and polycyclic aromatic hydrocarbons (especially benzo[a]pyrene) in PM10, typically tracked at industrial-source monitoring stations.
Source: European Environment Agency Air Quality e-Reporting Database, Dataflow E1a.
Source: World Health Organization Global Air Quality Guidelines, 2021 update.
Frequently asked questions
- Which pollutants does the EU regulate?
- The EU Ambient Air Quality Directive 2008/50/EC, supplemented by the 4th Daughter Directive 2004/107/EC, regulates seven outdoor air pollutants: PM2.5, PM10, NO2, ground-level ozone (O3), SO2, CO, and benzene. A separate directive adds target values for arsenic, cadmium, mercury, nickel, and polycyclic aromatic hydrocarbons.
- Why is PM2.5 considered the most harmful pollutant?
- PM2.5 (particles up to 2.5 µm) is the single highest-burden pollutant in Europe, attributable to about 238,000 premature deaths per year across the EU-27 (EEA Burden of Disease, 2022, modeled attributable estimates). The EU annual limit is 25 µg/m³ (falling to 10 by 2030); the WHO 2021 guideline is 5 µg/m³.
- What are the health effects of NO2 and ozone?
- NO2, primarily from diesel combustion, inflames the airways and is causally linked to new-onset asthma in children; the EU annual limit is 40 µg/m³ vs a WHO guideline of 10 µg/m³. Ground-level ozone, a secondary pollutant formed in sunlight, reduces lung function and triggers asthma exacerbations, peaking in Mediterranean summers.
- Why does benzene have no safe exposure threshold?
- Benzene (C6H6), from vehicle exhaust, petrol stations, and industrial solvents, is a WHO Group 1 carcinogen with no safe exposure threshold for leukemia risk. The EU annual limit is 5 µg/m³, but the operational health guidance is to reduce exposure to the lowest practicable level regardless of the legal limit.
- Are SO2 and CO still a concern in Europe?
- SO2, from coal and high-sulfur fuel combustion, is largely controlled in the EU since the 1990s Large Combustion Plant Directive, and its daily limit of 125 µg/m³ is rarely approached, though it still matters in industrial regions and shipping routes. CO, from incomplete combustion, binds to hemoglobin and reduces oxygen transport; indoor CO from faulty boilers is more dangerous than ambient outdoor CO.