Automatic monitoring of air quality

Air Quality data in Waverley has until now been posted monthly on WBC’s website. This has comprised date from monitoring devices known as Diffusion Tubes, sited at various locations in the borough.

Waverley has now let a new contract with Ricardo Energy and Environment for monitoring of automatic sensors. One of these is sited in Farnham at the junction of The Borough and South Street. The sensor takes readings of two pollutants:

  • Nitrogen dioxide gas, NO₂
  • Particles less than 10 micrometers (0.01 mm) in diameter, PM₁₀

Readings are taken every hour in real time with very high accuracy. Information from automatic monitoring was only previously made available by WBC when the annual Air Quality Report was issued, the last one of which was for 2016!

The new contract has allowed WBC to join their national website www.airqualityengland.co.uk which provides real time linkage to all the national network of automatic monitors and provides historic data (only since 01.12.18 in the case of the WBC sites) and current measurements as well as tools to graph and average the data with an assessment of the relative degree of pollution. From the website, go to ‘Select a local authority / customer’, and from the drop down menu select Waverley. This will give a map of Waverley showing the locations of the monitors. Click on the symbol in Farnham, this will give a summary panel from which ‘View full details and data’ gives access to real time and historic data.

As one would expect there are very large fluctuations in NO₂ and PM₁₀ both on an hourly basis and from day to day. There are statutory limits for both long term and short term levels of pollution.

For the long term, limits are generally set on the basis of annual mean levels of 40µg/m³ for both NO₂ and PM₁₀ .

For the short term, the criterion is that levels must not exceed a threshold too often.

  • For NO₂ the hourly mean level must not exceed 200µg/m³ more than 18 times a year.
  • For PM₁₀ the 24 hour mean level must not exceed 50µg/m³ more than 35 times a year.

This is a welcome development by WBC, which shows that our council is honouring the commitments made to The Farnham Society in relation to making air quality data available to all as soon as possible.

 

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