Skip to main content  

    ​​Calibrating monitoring equipment
    diffusion tube
    ​Diffusion Tube


The City of London Corporation has been monitoring air quality in the Square Mile since the 1960s. Monitoring initially focused on sulphur dioxide and black smoke in response to the introduction of the Clean Air Act. Since 2001 the City has been an Air Quality Management Area for nitrogen dioxide (NO2) and fine particles (PM10), so monitoring now focuses on these pollutants. The City's historic air quality data is summarised in the annual air quality reports.

NO2 Diffusion Tube Monitoring

You may have seen 'diffusion tubes' around the City which monitor nitrogen dioxide at over 60 locations and provide an annual average result; long term data is included in the​ City Corporation's annual reports​.

NO2, PM10 and PM2.5 Continuous Monitoring

The continuous analysers are used to monitor air quality 24-hrs a day at the following locations. Data is available in the annual reports and London Air Quality Network:

  • S​ir John Cass School - an urban background site (NO2, PM10 and PM2.5)
  • Beech Street - a roadside site (NO2 and PM10)
  • Upper Thames Street - a roadside site (PM10)
  • Walbrook Wharf, Upper Thames Street - a roadside site (NO2)
  • Farringdon Street - a roadside site (PM2.5)

Air Quality Data and Pollution Alerts

The amount of pollution in the City varies from day to day and information is available in a number of different sources:

  • The free CityAir App enables users to receive pollution alerts and to find low pollution routes around London.
  • See the London Air Quality Network website, to sign up for pollution alerts and also to find out more about recent and historic air quality data from the City's 'continuous' monitoring stations. (The London Air Quality Network was formed in 1993 to co-ordinate and improve air pollution monitoring in London and is operated and managed by the Environment Research Group at King's College London)