Infrared absorption by atmospheric aerosol substances

Transmission spectra of natural aerosol substances have been obtained from λ2.5 to 15 μm (4000 to 666 cm−1) by the potassium bromide pellet technique; and the spectral variation of the absorption coefficient and the imaginary part of the refractive index of typical aerosol fractions, which includes sea salt and ammonium sulfate, is presented. Some data for the visual range are discussed. The aerosol fractions, i.e., dry water solubles (evaporation residues), dust (minerals), soot, and benzene solubles, have been obtained primarily from rain and snow water. The structured spectra of water solubles from tropical and mid-latitude rains (and aerosol filters) and their concentration are generally similar though more variable in snow, especially in the arctic and in arctic glacier ice. Absorption by dust and soot is less dependent on wavelength, and the influence of soot percentage and water content on ir aerosol absorption has been calculated. Problems of ir spectroscopy, such as the dependence of absorption coefficients on concentration in the KBr technique, and mixing effects, are also mentioned. Concentration and absorption spectra of alcohol and benzene extract of dry water solubles indicate that hydrocarbons play a more important role in air chemistry, especially in arctic regions, than previously assumed.