Answer · confidence: partial
How can sideways light tell gas molecules apart from dust specks?
Research question: How does the polarization of light scattered at 90 degrees differ between Rayleigh and Mie scattering, and how can this be used to distinguish between gas molecules and aerosols in the atmosphere?
The verified facts do not give polarization values at exactly 90 degrees, so this comparison is only partly answered. They do state that Mie scattering tends to be less polarized than Rayleigh scattering, especially at low phase angles 2, and that Mie theory predicts an excess of scattered light in the forward direction, unlike the molecular pattern 1. For separating the two, the records show that aerosol effects have a weaker wavelength dependence than Rayleigh scattering and are most visible in the red band 4, and that a polarization depression present in red but absent in blue indicates aerosol scattering 6. The newest fact is dated 2020 1, roughly six years before October 2026, so it may not reflect current conditions.
Checked 2026-10-13. Only documented and supported facts are used.
Dig deeper on this questionSources
[1] supported
Mie theory predicts that aerosol particles scatter light with an excess in the forward direction, which is distinct from the molecular (Rayleigh) scattering pattern.
"according to Mie theory, aerosol particles have an excess of light scattering in the forward direction, multiplying the dawn segment glow."Post-Volcanic Aerosol Altitude and Particle Size Measurements Basing on Twilight Sky Polarimetry
[2] supported
Mie scattering tends to have less polarization than Rayleigh scattering, especially at low phase angles.
"It is normal for Mie scattering to be excessive at low phase angles and have less polarization compared to Rayleigh scattering."Stratospheric Aerosol Particles Size Distribution Based on Multi-Color Polarization Measurements of the Twilight Sky
[3] supported
Increased aerosol loading lowered the sky's zenith polarization across the whole twilight, including the dark stage.
"In autumn 2019, polarization was lower during the whole twilight period including the dark stage, when the troposphere and stratosphere are immersed in the shadow of the Earth."Post-Volcanic Aerosol Altitude and Particle Size Measurements Basing on Twilight Sky Polarimetry
[4] supported
Aerosol (Mie-type) effects show a weaker wavelength dependence than Rayleigh and multiple scattering, so they are expected to be most visible in the red band.
"Due to weaker wavelength dependency compared to Rayleigh and multiple scattering, the aerosol effects are expected to be most noticeable in the red spectral band."Stratospheric Aerosol Particles Size Distribution Based on Multi-Color Polarization Measurements of the Twilight Sky
[5] supported
With more aerosol, the polarization of multiple scattering was significantly lower than in clear-atmosphere conditions, which is the main reason for the drop in twilight polarization.
"In the case of an increased aerosol level in 2019, multiple scattering polarization is significantly less than in the case of the clear atmosphere in 2018, being the primary reason for a decrease in polarization during the light twilight."Post-Volcanic Aerosol Altitude and Particle Size Measurements Basing on Twilight Sky Polarimetry
[6] supported
Polarization depression in the red band that is absent in the blue band indicates aerosol scattering, since the aerosol's depolarization is distinguishable from Rayleigh behavior.
"polarization depression in the R band that is not noticed in the B band."Stratospheric Aerosol Particles Size Distribution Based on Multi-Color Polarization Measurements of the Twilight Sky
[7] supported
The retrieved mean aerosol particle radius of 0.11 μm is typical of background or moderate eruption conditions, which helps characterize the aerosol particles.
"The mean radius of (0.11 μm) is typical for background or moderate eruption conditions, however, aerosols were mostly observed in the upper troposphere and near the tropopause rather than in the stratosphere."Post-Volcanic Aerosol Altitude and Particle Size Measurements Basing on Twilight Sky Polarimetry
[8] supported
The polarization depolarization effect attributed to stratospheric aerosol occurs when the effective scattering altitude is about 20 km, corresponding to the Junge layer.
"This depolarization takes place when the effective altitude of scattering is about 20 km, that corresponds to the Junge layer."Stratospheric Aerosol Particles Size Distribution Based on Multi-Color Polarization Measurements of the Twilight Sky
[9] supported
Twilight sky polarization was used to detect aerosol from the Tavurvur (Rabaul) volcano in 2006.
"Twilight sky polarization is sensitive to aerosol scattering, and this fact helped to detect the aerosol from the Tavurvur (Rabaul) volcano in 2006"Stratospheric Aerosol Particles Size Distribution Based on Multi-Color Polarization Measurements of the Twilight Sky