Coarse-Mode Aerosols over Bright Surfaces: Challenges and Uncertainties

Satellite remote sensing has greatly advanced our understanding of global aerosol distributions, yet substantial uncertainties persist over dryland regions where coarse-mode aerosols and bright heterogeneous surfaces remain particularly challenging for current retrieval algorithms. Validation frameworks that rely heavily on AERONET are spatially imbalanced, with drylands markedly underrepresented, leading to systematic biases and overly optimistic global performance assessments. Our analysis shows that disagreement between major satellite aerosol optical depth products is disproportionately concentrated in drylands with low Ångström Exponent values, highlighting coarse-mode dominant regions as a critical blind spot in global aerosol monitoring. We discuss key retrieval challenges and outline priorities for algorithm development, expanded observations, and stratified validation strategies to better constrain aerosol radiative effects and climate impacts over drylands.