Infrared Optical Constants of Ammonium Sulfate, Sahara Dust, Volcanic Pumice, and Flyash

Spectra of the real and imaginary parts of the refractive index m = n ' - in from 2.5 microm to 40 microm of ammonium sulfate, Sahara dust (as collected at Barbados), volcanic dust (pumice), and dust from a coalfired power plant are presented. With a peak absorption index n = 1.0 at 10 microm Sahara dust turns out to be the strongest absorber in the atmospheric window. The dispersion of n' is also very pronounced near 9 microm and 20 microm. Volcanic and coal-fire dust also absorb in the window region stronger than most of our earlier-investigated more normal aerosol fractions. The data for ammonium sulfate are compared with Remsberg's measurements on an aqueous solution.