Spectral Transmission Properties (0.35–25 µm) of Some Anthropogenic and Natural Atmospheric Aerosol Constituents

Atmospheric aerosols can have wide-ranging effects on the Earth’s atmosphere, hydrosphere, and biosphere. To help improve our understanding of these effects, we have conducted spectral reflectance and transmission properties of a suite of anthropogenic and natural aerosols across a wide wavelength range (0.35–25 microns). Our sample suite included rock and mineral dusts, sulfates and nitrates, ocean water precipitates, and a variety of carbonaceous and organic materials. These data are useful to identify species that may be present in the atmosphere from spectroscopic measurements. Different aerosol/dust species can have unique spectroscopic properties in terms of diagnostic absorption bands and spectral shapes, and diagnostic absorption bands, can be present in multiple wavelength regions, including within atmospheric transmission windows. The composition of aerosol species can be determined with varying degrees of specificity from their spectroscopic properties. Increases in aerosol abundance, which may lead to saturation of strong absorption bands can be partially compensated for by accompanying strengthening of “secondary” absorption bands that are normally weak. Grain size variations mostly affect absorption/transmission intensities, but do not lead to the appearance of any new absorption bands. Empirical laboratory studies, where grain size and concentration are varied, can provide information that can be used to determine atmospheric aerosol composition and to help constrain measurements and models of atmospheric optical depth.