Although the currently available open-path monitoring systems vary considerably from one another in terms of function and design, all of these systems operate using the same basic principle. All of these devices are designed to detect and characterize air pollution by measuring the absorption of light energy caused by airborne chemicals as they pass through a beam of projected light.
With many of these instruments, we don't really have a clue as to the specifics of how they work. In a stroke of incredible luck, however, our friends at CBE were able to purchase an older version of ETG's "Air Sentry" FTIR monitor, and we have been able to work extensively with this system.
Our hands-on experience with the operation of the FTIR monitor, and the knowledge we gained from this experience, proved to be invaluable to us in our negotiations with the refinery over the design for a permanent fenceline monitoring system. We have included some examples of the work we have done with spectra from the refinery as a way of introducing the science of FTIR spectroscopy.
Please keep in mind that we can in no way be considered authorities in this field. We include the following examples as a way to try to share a little of what we have learned.