Infrared extinction spectra of some common liquid aerosols

Infrared extinction spectra in the 3-5-microm and 7-13-microm atmospheric window regions have been obtained for smokes of petroleum oil, sulfuric acid, and phosphoric acid of varying droplet concentration and for water fogs. Spectra were also obtained at 0.36-2.35microm for petroleum oil and sulfuric acid smokes. Experimental results were compared, for sulfuric acid and water aerosols, to calculated values obtained from the Mie theory. Agreement was as good as +/-10%. When absorbing smoke droplets are small compared to wavelength, very useful approximations apply, and droplet clouds may be spectrally simulated by thin liquid films. In such cases, the imaginary component of refractive index may be approximated directly from aerosol spectra. At 12.5-microm wavelength, water fog extinction is nearly independent of droplet size distribution, suggesting a simple scheme for measurement of total liquid water content of an optical path.