In recent years open-path FTIR systems (active and passive) have demonstrated great potential and success for
monitoring air pollution, industrial stack emissions, and trace gas constituents in the atmosphere. However,
most of the studies were focused mainly on monitoring gaseous species and very few studies have investigated
the feasibility of detecting bio-aerosols and dust by passive open-path FTIR measurements. The goal of the
present study was to test the feasibility of detecting a cloud of toxic aerosols by a passive mode open-path
FTIR. More specifically, we are focusing on the detection of toxic organophosphorous nerve agents for which
we use Tri-2-ethyl-hexyl-phosphate as a model compound. We have determined the compounds' optical
properties, which were needed for the radiative calculations, using a procedure developed in our laboratory. In
addition, measurements of the aerosol size distribution in an airborne cloud were performed, which provided the
additional input required for the radiative transfer model. This allowed simulation of the radiance signal that
would be measured by the FTIR instrument and hence estimation of the detection limit of such a cloud.
Preliminary outdoor measurements have demonstrated the possibility of detecting such a cloud using two
detection methods. However, even in a simple case consisting of the detection of a pure airborne cloud,
detection is not straightforward and reliable identification of the compound would require more advanced
methods than simple correlation with spectral library.