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Monitoring Air Pollution

Air monitoring methodologies can be divided into five main types, covering a wide range of costs and performance levels. The methods and their relative merits are shown in the table below and discussed in the following section. The use of a particular type of monitoring equipment may need to be justified in review and assessment reports and therefore should be chosen appropriately.

It is also important to choose the most appropriate monitoring location for investigating a specific air pollution source or problem.

Passive Sampling

Methods (Diffusion Tubes) -These represent a simple and cost-effective method of monitoring air quality in an area, to give a good general indication of average pollution concentrations. They are, therefore, particularly useful for assessment against annual mean objectives. A sample integrated over the exposure time is collected by diffusion to the sampler. The low cost per tube permits sampling at a number of points in the area of interest; this is useful in highlighting hot spots of high concentrations, such as alongside major roads. They are less useful for identifying 'hot spots' around point sources or near to industrial locations where greater temporal resolution is required for particular objectives. Diffusion tubes surveys are simple to undertake and minimal operator training is required. Diffusion tubes are available for the following pollutants in the Air Quality Strategy:

  • Nitrogen dioxide
  • BTX (benzene, toluene, xylene)
  • 1,3-butadiene
  • (Sulphur dioxide (not suitable for R&A)

The tubes must be analysed by laboratories that can offer suitable quality assurance and quality control measures to ensure the results meet the data quality objectives defined for the method (contact the Monitoring Helpdesk for a list of suppliers and analysers of diffusion tubes). The diffusion tube data may be corrected for bias in the analytical results.