Remote identification of in situ atmospheric silicate and carbonate dust by passive infrared spectroscopy

The authors report the remote identification of in situ airborne silicate (Si/sub X/O/sub Y/) and carbonate (CO/sub 3/) dust using passive infrared spectroscopy. The silicates are identified based on the 9.7 /spl mu/m emission feature, a resonance due to the fundamental asymmetric vibrational mode of the O-Si-O structure. The carbonate structure from calcite (CaCO/sub 3/) was identified based on the CO bending mode resonance at 11.4 /spl mu/m. Laboratory spectra of dust collected after the event confirm the high silica and carbonate content. Minimum detectable column densities are about 10/sup -6/ to 10/sup -7/ g/cm/sup -2/. These will be limited by the signal-to-noise ratio (SNR) of the detection system and the change in the refractive index across the spectral feature. The technique is useful for quick, first-order identifications of aerosol clouds when in-situ probes are unavailable or when the origin (hence probable composition) of the cloud is not known.