Three main methods are available to measure air pollution:
Passive Sampling: This refers to diffusion tubes that provide a simple and inexpensive indication of average pollution levels over a period of weeks or months. Plastic tubes, 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.
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.