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_XO_Y) and carbonate (CO₃) dust using passive infrared spectroscopy. The silicates are identified based on the 9.7 μm emission feature, a resonance due to the fundamental asymmetric vibrational mode of the O-Si-O structure. The carbonate structure from calcite (CaCO₃) was identified based on the CO bending mode resonance at 11.4 μm. Laboratory spectra of dust collected after the event confirm the high silica and carbonate content. Minimum detectable column densities are about 10^-6 to 10^-7 g/cm^-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