Answer · confidence: partial
How do scientists estimate the amount and size of dust or sea spray in the air from ground-based sky color readings?
Scientists retrieve aerosol size distributions from ground-based measurements of solar transmission and sky radiance taken in a horizontal plane through the Sun 2. The sky-based retrieval gives the size distribution and scattering phase function, averaged over the whole atmospheric column 4. Coarse particles, which would include dust and sea-salt-type aerosol, appear as a distinct mode in the measured size distributions, and systematic inversion is applied to dust and maritime aerosol to relate size distribution to optical properties 58. The color-index method is used to detect stratospheric aerosol, and twilight geometry isolates a sunlit altitude, but the records do not show how these color readings are converted into dust or sea spray amounts 611. The newest fact comes from a 2022 review, about four years old as of October 2026 7, so the answer is only partly supported.
Checked 2026-10-21. Only documented and supported facts are used.
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[1] supported
Scientists retrieved vertical profiles of aerosol extinction in the lower stratosphere and upper troposphere from ground-based twilight sky brightness measurements using the Levenberg–Marquardt algorithm.
"Aerosol extinction vertical profiles in the lower stratosphere-upper troposphere were retrieved with the help of the Levenberg–Marquardt algorithm."Raikoke aerosol clouds observed from Tbilisi, Georgia and Halle, Belgium using ground-based twilight sky brightness spectral measurements. (2020)
[2] supported
Scientists retrieve aerosol size distributions from ground-based measurements of solar transmission and sky radiance taken in a horizontal plane through the Sun.
"Ground‐based measurements of the solar transmission and sky radiance in a horizontal plane through the Sun are taken in several geographical regions and aerosol types: dust in a desert transition zone in Israel, sulfate particles in Eastern and Western Europe, tropical aerosol in Brazil, and mixed continental/maritime aerosol in California."Size distribution and scattering phase function of aerosol particles retrieved from sky brightness measurements (1994)
[3] documented
Lognormal and gamma size distributions of aerosols can each be described by two parameters, the effective radius and the effective variance.
"Both the lognormal and gamma size distributions can be determined by two parameters, the effective radius and effective variance."Accounting for dust aerosol size distribution in radiative transfer (2015)
[4] supported
The sky-based retrieval yields the size distribution and scattering phase function of aerosol particles, representing an average over the entire atmospheric column.
"The retrieved properties represent an average on the entire atmospheric column."Size distribution and scattering phase function of aerosol particles retrieved from sky brightness measurements (1994)
[5] supported
Coarse particles, which would include dust and sea-salt-type aerosol, appear as a distinct mode in the measured volume size distributions, separate from fine sulfate particles.
"The measured volume size distributions before the injection of stratospheric aerosol consistently show two modes, sulfate particles with r m < 0.2 μm and coarse particles with r m > 0.7 μm."Size distribution and scattering phase function of aerosol particles retrieved from sky brightness measurements (1994)
[6] supported
Scientists use the ratio of brightness in two sky color channels (a color index) measured at different sky points and solar zenith angles to detect stratospheric aerosol.
"Here I is the background intensity, ζ is the sky point position in the solar vertical, z is the solar zenith angle, R and B are the color channels."Background Stratospheric Aerosol Investigations Using Multi-Color Wide-Field Measurements of the Twilight Sky
[7] supported
Ground-based sky radiance measurements can be inverted to retrieve aerosol optical properties, using a flexible inversion algorithm (a method cited in the reference list, not explained in the text).
"Dubovik, O. & King, M. D. A flexible inversion algorithm for retrieval of aerosol optical properties from Sun and sky radiance measurements."Scattering and absorbing aerosols in the climate system (2022)
[8] supported
Systematic inversion of sky measurements is applied to key aerosol types including dust and maritime aerosol to relate their size distribution and phase function to optical properties.
"Systematic inversion for the key aerosol types (sulfates, smoke, dust, and maritime aerosol) of the size distribution and phase function can give the relationship between the aerosol physical and optical properties that can be used to compute the radiative forcing."Size distribution and scattering phase function of aerosol particles retrieved from sky brightness measurements (1994)
[9] supported
The accuracy of aerosol optical properties retrieved from AERONET Sun and sky radiance measurements has been assessed in a study cited by this review.
"Dubovik, O. et al. Accuracy assessments of aerosol optical properties retrieved from Aerosol Robotic Network (AERONET) Sun and sky radiance measurements."Scattering and absorbing aerosols in the climate system (2022)
[10] supported
Fitting the scattering angle dependence to a lognormal size distribution gives a median stratospheric aerosol particle radius of about 0.08 microns with a width of 1.5 to 1.6.
"This is used to find the parameters of lognormal size distribution: median radius about 0.08 microns and width 1.5-1.6 for stratospheric altitude range."Background Stratospheric Aerosol Investigations Using Multi-Color Wide-Field Measurements of the Twilight Sky
[11] supported
Twilight geometry lets observers isolate a specific atmospheric altitude that is still sunlit while lower layers are in the Earth's shadow, which sets the effective scattering altitude used in the estimate.
"Twilight geometry of radiation transfer allows separating the definite atmospheric level still illuminated by the Sun while lower dense layers are immersed into the Earth's shadow."Background Stratospheric Aerosol Investigations Using Multi-Color Wide-Field Measurements of the Twilight Sky