How do we monitor air pollution?

Air pollution is monitored at certain sites around Wales 24 hours a day. There are many different ways of sampling the air to check how polluted it is.

There are 5 main methods of sampling air quality:


Passive Monitoring

  • Diffusion tubes absorb a specific pollutant from the ambient air  - no power supply is needed
  • Diffusion tubes normally monitor for 2-4 weeks at a time
  • The tubes must be sent to a laboratory for analysis to see how much pollution they have detected
  • Semi-automatic sampling

Active (Semi Automatic) Sampling

  • An analyser pulls the ambient air through a filter for a set period of time e.g  one filter per day
  • The filters are then collected and sent to a laboratory for analysis to see how much pollution they have detected
  • Automatic monitoring point

Automatic point monitoring

  • Ambient air is pulled through an analyser which recognises the chosen gas and will calculate its concentration
  • Automatic sites monitor pollutants 24hours a day

Photochemical and optical sensor systems

  • These are portable monitoring tools that can continuously monitor a range of pollutants. The sensors are of low sensitivity and mostly suitable for identifying hotspots at roadsides and near point sources.
  • Data can be downloaded to your computer and analysed.

Remote optical/long-path monitoring

  • This method of sampling detects pollution between a light source and a detector which are placed separately at a site
  • Real time measurements can be taken with this type of sampling.
  • Data can be sent from the analyser directly to your computer which means it can be seen instantly.