Air pollutants explained
Find out where particles and gases come from, what their concentrations mean and which ones determine the European AQI.
PM2.5Fine particles
PM10Inhalable particles
NO₂Nitrogen dioxide
O₃Ground-level ozone
SO₂Sulphur dioxide
COCarbon monoxide
Particles and gases
PM2.5 and PM10 describe the size of particles suspended in air. Some particles come directly from combustion or dust. Others form in the atmosphere as gases react. Nitrogen dioxide, ozone, sulphur dioxide and carbon monoxide are gases with different sources and behaviour.
PiSpace Air labels concentrations with their units and time period. A larger number for one pollutant does not imply a higher index band than a smaller number for a different pollutant. The European AQI uses separate thresholds for each of its five pollutants.