Monitoring In Spelthorne

Nitrogen dioxide and particulate matter are monitored in the Borough at three continuous monitoring stations and a network of diffusion tubes. Nitrogen dioxide is the principal pollutant of concern in the Borough and the most extensively monitored.

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How do we monitor?

There are two techniques used in this Borough:

• diffusion tubes
• Continuous Monitoring Stations

Diffusion tubes are a simple and cost-effective method of monitoring. It is a plastic tube (about the size of a finger) which can be attached to a lamp post. Material within the tube is covered in a special coating. The tube is exposed to air at a chosen location over a period of a month. The coating absorbs nitrogen dioxide and so it is possible to find out an average level of nitrogen dioxide present at that location during that month. At the end of each month, the tubes are sealed and then sent off for analysis to an independent laboratory.

The results from each month are then used to work out an average level of nitrogen dioxide for a year. Results from diffusion tubes can only be compared to the annual mean objectives for the pollutants. They are not as accurate and precise as continuous monitors but give a good general indication of average pollutant levels.

A continuous monitoring station is an enclosure that contains one or more instruments to measure air quality continuously. They can vary greatly in size from a small cabinet right up to a walk in container depending on the number and type of instruments held there to measure air quality. The equipment is capable of measuring air quality continuously and results can be available in real time. Results can be averaged over short time periods such as 15 minutes, an hour or 24 hours.

Spelthorne Monitoring Results

An 

 can be downloaded. Previous years are available on request.

Raw and bias adjusted monitoring data can be downloaded as follows:

Operational sites

There are three continuous monitoring stations in Spelthorne (Oaks Road, Stanwell; Sunbury Cross and Haslett Road, Upper Halliford) and over 50 diffusion tube monitoring locations.

Data for the Oaks Road and Sunbury Cross stations are available from the Heathrow AirWatch website. Data for Haslett Road is available upon request. 

Data for the Council's diffusion tube network:
 

Closed sites

• the continuous monitoring station at Sunbury Cross previously operated between 2007 and April 2012;
• a continuous monitoring station at junction 13 of the M25 motorway operated between 2004 and 2010 by Highways England;
• three diffusion tube monitoring locations near motorways between 2008 and 2010 maintained by Highways England;
• a one-year diffusion tube survey in 2010 at about 20 locations near Heathrow; and
• BTEX diffusion tube monitoring on Long Lane, Stanwell operated in 2010 and 2011

Please contact the Pollution team if you would like data relating to these past surveys.

Bias Adjustment Factors

The bias adjustment factor is the method bias between diffusion tube monitoring and the results of a continuous monitor.

In Spelthorne this is calculated from triplicate diffusion tubes located at the Oaks Road, Stanwell continuous monitoring station, except 2012 when the factor from the national bias adjustment spreadsheet was used.

Our bias adjustment calculation spreadsheet can be downloaded for 2023. Earlier spreadsheets can be made available on request.