Which dust or salt fades blue skies most, and how do scientists measure it?

Research question: Which airborne particles, such as dust, smoke, or sea salt, most strongly wash out the blue of a sky, and how do scientists estimate their size and amount from the ground?

The facts do not single out one particle type as the strongest washer of sky blue. They list aerosols generally, including fine dust, pollen, smoke, soot, salt crystals, smog, droplets, and volcanic ash ¹. Particles about the size of light's wavelength scatter white sunlight, and because aerosol and water concentration is higher near the ground, the whitish blue is most visible near the horizon ³⁶. To estimate amount, the records point to aerosol optical depth as a key measure ², and ground-based sunphotometers measure aerosol optical thickness ⁵; ground-based remote sensing is said to meet WMO traceability requirements in over 95% of measurements ⁴. The facts do not explain how particle size is estimated from the ground, though Mie scattering theory describes scattering by spherical particles of roughly wavelength-sized diameter ⁷. The newest dated source covers data through 2023, so it is about three years old relative to October 2026 ².

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