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Air Pollution Sampling Methods

Air samples are collected to find out the concentration of pollutants in the air. There are four types of air pollutant testing, each having their own positive attributes. The systems vary depending on the need for portability, as well as the type of pollution being searched for.

  1. Passive Sampling

    • Passive sampling is used to get an indication of pollution levels over a period of a few weeks to months. Sampling of this type is performed near major roads or near power generation sites to detect levels of nitrogen dioxide and benzene. This type of sampling method is not accurate enough to detect direct sources of pollution. It is used to get an idea of average pollution levels.

      Passive sampling does not use a physical pump for air collection. Instead a tube housing the sample collector is mounted in the area to be tested, allowing the normal air flow to move through the tube. At the end of the sample period, caps are placed on the ends of the tube and the unit is taken for lab analysis.

    Active Sampling

    • Active sampling is the same as passive sampling, except this method uses a pumping mechanism. The air is physically pushed through a filter, or chemical solution, to obtain the sample for later testing in the lab. Air flows over the filter at a specific rate (volume) for a set amount of time. Using this method allows the lab to calculate the amount of pollutant in the air. Switching sample catchers in the unit enables the tester to test for specific pollutants in the given area, and can be done on a daily basis.

    Automatic Sampling

    • Use of automatic sampling is designed for a single point sample such as factory smoke stacks. These are sophisticated pieces of equipment producing high-resolution measurements. Using methods such as spectroscopy and gas, the samples are analyzed on-line in real-time in order to produce accurate data showing pollution levels. These units require high standards of calibration and operational procedures to ensure reliability.

      Common pollutants that are detected by automatic samplers are benzene, carbon monoxide, ozone, sulphur dioxide as well as oxides of nitrogen. As with all pollution sampling, the information is sent to the region's environmental agency for monitoring and pollution standards assessment.

    Optical Analysers

    • A beam of light is sent from the emitter to the detector. Analyzing the wavelength of the light will show what pollution is in the air. All molecules absorb light at different rates and wavelengths. Analyzing the difference in the light can show what molecules are in the path, allowing the tester to determine the amount of pollutant in the air.

      Differential Optical Absorption Spectroscopy (DOAS) uses a long path (detector is far away) spectroscopic technique to get real-time measurements of the concentration of pollutants. Spectroscopy can be used in the detection of known pollutants as long as the light absorption rates are known.

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