Passive Diffusion Tubes

Techniques used to monitor air quality in the Vale.

Air quality in the Vale is generally good. There is however one pollutant of potential concern. This is Nitrogen Dioxide (NO₂). Monitoring of NO₂ is undertaken by:-

• Passive diffusion tube. This is a simple and relatively inexpensive device consisting of a plastic tube which can be attached to street furniture (eg a street light) allowing a sample of air to be collected (over a recorded exposure period) by diffusion into the sampler. The tubes are sealed and then sent off for quantitative analysis. They give a good indication of long term spatial and temporal trends in pollutant levels.

• Automatic real-time monitor. This produces high-resolution measurements over a short averaging period eg 15 minutes. The air sample is analysed in real-time. This method offers continuous data, which identifies peaks and troughs during a short period eg 24 hours, as well as long term averages. This method is also accurate and reliable enough to inform the decision making process in terms of identifying problem areas.

Date Updated: 23/04/08