The seven regulated EU air pollutants

PM2.5, PM10, NO2, O3, SO2, CO, and benzene — what each pollutant is, where it comes from, and how exposure affects health.

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 10 µg/m³, WHO 2021 guideline 5 µg/m³. PM2.5 is the single highest-burden pollutant in Europe, attributable to about 380,000 premature deaths per year across the EU+UK region (EEA, HRAPIE methodology).

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 (validated annual).

Source: World Health Organization Global Air Quality Guidelines (2021 update).

Sources: European Environment Agency Air Quality e-Reporting; WHO Global Air Quality Guidelines 2021; EU Directive 2008/50/EC and the revised Directive (EU) 2024/2881; Copernicus Atmosphere Monitoring Service.