We have followed the Defra Local Air Quality Management Guidance (also referred to as LAQM TG16) when considering which monitoring methods to use. In Bristol, the majority of monitoring that has been carried out to date focuses on NO2 and particulate matter.
NO2 concentrations have been measured in two ways:
- continuous monitoring stations – these record data in real-time, but are expensive to install and maintain.
- diffusion tubes – these are cost-effective monitors that provide a wider coverage of NO2 concentrations but need to be replaced every month and that provide a better spatial coverage of NO2 concentrations.
Both monitoring methods are accepted by LAQM TG16.
The standard of instruments that can be used by local authorities is prescribed in LAQM TG16, and due to the difficulty of measuring concentrations of nitrogen dioxide in the parts per billion range, low cost sensors are not appropriate to use for this pollutant.
Particulate matter can be monitored using a large number of different technologies, but mainly by continuous monitors. Although newer, low-cost sensors have appeared in the market in recent years, they have not all received approval from Defra and large uncertainties remain over their performance.