Dust aerosol optical depth at thermal infrared wavelength from an AeroCom/AeroSat study: Comparative analysis and perspectives

Abstract. Mineral dust interacts with Earth’s radiation across a broad spectral range, from near UV to the thermal Infrared (TIR). While global distributions of dust optical depth at mid-visible wavelength (at 0.55 μm, DOD_0.55) are well characterized by remote sensing and models, corresponding TIR products (at 10 μm, DOD₁₀) remain limited to a few satellite retrievals and are rarely simulated by models. This coordinated AeroCom–AeroSat study addresses these gaps by presenting the current state of DOD₁₀ using four satellite TIR products, six AeroCom model simulations, a model-based, observation-constrained climatological database, and laboratory measurements of dust properties. The analysis reveals substantial differences in DOD₁₀ across satellite products and models, sometimes exceeding a factor of ten. Discrepancies among satellite products may link to retrieval algorithms and assumptions, while model differences arise from dust emission, removal processes, and mass extinction efficiencies determined by dust optical properties and size distributions. Multi-model mean results indicate that coarse-mode dust (diameter > 2.5 μm) accounts for nearly 80 % of dust mass loading and DOD₁₀ but only about 40 % for DOD_0.55. The absence of a reference dataset for DOD₁₀ poses a major challenge, limiting validation to indirect comparisons with proxies such as AERONET coarse-mode AOD_0.55, which is informative but insufficient for DOD₁₀ validation. Laboratory measurements of spectral-dependent optical properties highlight the potential of combining shortwave and longwave remote sensing to advance dust compositions analysis through their distinct spectral sensitivities.