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Updated: Jun 15, 2026

Non-equilibrium Microwave Plasma for Efficient High Temperature Chemistry
Published on: August 1, 2017
Correct equations and common approximations for calculating Rayleigh scatter in pure gases and mixtures and
1National Oceanic and Atmospheric Administration Earth System Research Laboratory, 325 Broadway, Boulder, Colorado 80305, USA. wynn.eberhard@noaa.gov
Abstract:
Equations for Rayleigh scattering in a mixture of gases are derived and compared to frequent approximations in the literature. The traditional Rayleigh scattering equation as modified by King for scatter from a pure gas is correct, whereas another version sometimes appearing in modern literature is erroneous. Use of a mixture's refractive index, which is equivalent to assuming the isotropic molecular polarizabilities of the component gases are identical, is an approximation. Another common approximation is using only number-density weighting of the King factors. Approximation errors can be large when the major components of a mixture have disparate optical properties. Fortunately, the errors for Earth's air are much smaller and comparable to errors from other sources.
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