Frequently asked questions
How do you measure air pollution?
Three main methods are available to measure air pollution:
- Passive Sampling:
This refers to Diffusion tubes or badges that provide a simple and inexpensive indication of average pollution levels over a period of weeks or months. Plastic tubes or discs, open at one end to the atmosphere and with a chemical absorbent at the other, collect a sample for subsequent analysis in the laboratory. The low cost per tube allows sampling at a number of points and is useful in highlighting "hotspots" where more detailed study may be needed.
- Active Sampling:
This involves the collection of samples, by physical or chemical means, for subsequent laboratory analysis. Typically, a known volume of air is pumped through a filter or chemical collector for a known period of time - the collector then subjected to laboratory analysis.
- Automatic Sampling:
This is the most sophisticated method producing high-resolution measurements of a range of pollutants at a single point. The sample is measured on-line and in real-time, typically with 15-minute averages or better, with data being collected from individual monitoring sites by telemetry. Instruments using physical scientific measurement techniques, such as chemiluminescence, UV fluorescence, IR absorption and Differential Optical Absorption Spectroscopy (DOAS), are used.
All of these techniques outlined above are employed in the air quality monitoring undertaken in Swansea.