Infrared optical properties of phosphorus-derived smoke

The reaction of elemental phosphorus with atmospheric oxygen and water vapor produces a highly visible white smoke; extinction spectra in the 7-14-microm infrared have been measured for such phosphorus-derived smokes in varying environmental conditions. The extinction spectra show that the smoke particles are not homogeneous droplets of o-phosphoric acid. A descriptive model of the formation of the phosphorus-derived smoke particles is proposed; this model describes the smoke particles as chemically quasi-stable radially inhomogeneous layered spheres of condensed phosphoric acids. The dependence of phosphorus-derived smoke extinction on relative humidity is described, and extinction spectra taken over a 280-min time period show that the smoke evolves toward an o-phosphoric acid aerosol. The relative humidity and time-dependent smoke extinction spectra are compared with o-phosphoric acid extinction spectra computed from Lorenz-Mie theory. The optical constants of the phosphorus-derived smoke are found from the extinction spectra as functions of relative humidity and time.