Passive Monitoring

Passive Air Quality Sampler (PAQS)

Our PAQS is composed of chemically treated filters that absorb target compounds. After filters are exposed to the environment, they are analyzed in our Clean Air Laboratory to measure pollution concentrations collected for the duration of exposure.

Sampling filter media is currently available for:

  • Sulphur dioxide (SO2)
  • Hydrogen sulphide (H2S)
  • Ozone (O3)
  • Nitric oxide (NO) and Nitrogen dioxide (NO2)
  • Volatile Organic Compounds (VOC's)
  • BTEX

The sampling system allows for up to four samplers, consists of a rain shelter, mounting hardware and room inside for storing on-site blanks. One shelter can support duplicate sampling of two parameters.

This system provides a cost-effective method for collecting air quality data. It does not require power, making it an excellent tool for sampling in regions that are remote or local, large or small. Additionally, PAQS provides the advantage of easy operation for simple and easy sampling. The system is portable, does not require electricity, data loggers or pumps and ensures that there is no active movement of air through the sample. The sampling system has a protective rain shelter and is a cost-effective solution when conducting passive air monitoring.

Passive sampling devices operate on the principles of absorption and permeation, physically binding to the specific compounds that are being targeted. Air pollutants that are being sampled will diffuse or permeate through a semi-permeable membrane and then collect on a filter that has been chemically treated to absorb those targeted compounds. After being exposed, the sample is analyzed in the laboratory for the amount of the targeted compound collected. An average concentration is then calculated based on the duration of exposure (accounting for the effects of relative humidity, temperature and wind speed).


Passive monitoring is available for use as an alternative and complementary to the continuous monitoring analyzers in numerous applications such as:

  • Measuring large areas for spatial variation of pollutant levels.
  • Studying long-term trends.

Compliance or regulatory monitoring is the most common form of use. Results can be utilized in long-term trending of collected data and can be operated either independently or as part of a larger network of samplers. The PAQS can continue to be used for repeat sampling as the filters are submitted to our laboratory for analysis.

Clean Air Laboratory

Laboratory analysis for our Passive Air Quality Monitoring System is performed in our state-of-the-art, positive pressure, Clean Air Laboratory. Ventilated air is first passed through a multi-stage HEPA filtration system which removes 99.99 per cent of all particles in the air. After passing through the filtration system, the air is then directed through a chemical scrubber which removes any air contaminants such as Ozone, Hydrogen Sulphide, Sulphur Dioxide and others.

Our air laboratories are designed to meet all US EPA and European Union standard requirements for temperature and humidity, which are precisely controlled through a computerized access panel. In this way we ensure that no contamination will come into contact with the passive monitors and that our laboratory controls are of the highest quality possible.