In active open-path FT-IR air monitoring, the composition of air is analyzed by passing a beam of broadband infrared light through the air and noting the characteristic infrared absorption bands created by the molecular compounds within it.
Open-path FT-IR air monitoring has many applications. The figure above shows how an infrared beam might be used to monitor fugitive gas emissions from leaky barrels. Open-path FT-IR air monitoring can be used to measure emissions from many types of sources, including highly localized sources of gas emissions such as the barrels shown in the figure above or more diffuse sources such as an entire chemical plant. The length of the infrared beam path can vary from less than one meter to more than 1000 meters. The downwind distance to the monitoring beam can be as great as a few miles if the levels of airborne analytes are high enough to allow detection at such a great distance.
A common application of open-path FT-IR air monitoring techniques is fenceline monitoring - that is, measuring the levels of fugitive emissions leaving a site across it's fenceline boundary. In these applications, infrared beam paths are typically a few hundred meters in length and are usually located within a few hundred meters of the source of emissions. Detection limits will vary for different analytes but are generally in the part-per-billion to part-per million range.
Follow the links below to see some examples of active monitoring applications, including photographs and examples of spectra, or for some references to off-site reading on the subject of open-path FT-IR air monitoring.
Examples of active FT-IR air monitoring
References and Suggested Reading
AeroSurvey's Web Site / AeroSurvey, Inc. / www.aerosurvey.com