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

TLDR

Spectra of the real and imaginary parts of the refractive index from 2.5 μm to 40 μm for ammonium sulfate, Sahara dust, volcanic dust (pumice), and coal‑fire dust are presented. The ammonium sulfate data are compared with Remsberg’s measurements on an aqueous solution. Sahara dust shows the strongest absorption in the atmospheric window with a peak n″ of 1.0 at 10 μm, while pronounced dispersion of n′ occurs near 9 μm and 20 μm, and volcanic and coal‑fire dust also absorb strongly in this region, surpassing many previously studied aerosol fractions.

Abstract

Spectra of the real and imaginary parts of the refractive index m = n′ − in″ from 2.5 μm to 40 μm of ammonium sulfate, Sahara dust (as collected at Barbados), volcanic dust (pumice), and dust from a coal-fired power plant are presented. With a peak absorption index n″ = 1.0 at 10 μm Sahara dust turns out to be the strongest absorber in the atmospheric window. The dispersion of n′ is also very pronounced near 9 μm and 20 μm. 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.