Abstract
Abstract. Accurate Rayleigh scattering and absorption cross sections of atmospheric gases are essential for understanding the propagation of electromagnetic radiation in planetary atmospheres. Accurate extinction cross sections are also essential for calibrating high-finesse optical cavities and differential optical absorption spectroscopy and for accurate remote sensing. In this study, we measured the scattering and absorption cross sections of carbon dioxide, nitrous oxide, sulfur hexafluoride, oxygen, and methane in the continuous wavelength range of 307–725 nm using broadband cavity-enhanced spectroscopy (BBCES). The experimentally derived Rayleigh scattering cross sections for CO2, N2O, SF6, O2, and CH4 agree with refractive index-based calculations, with a difference of (0.4 ± 1.2) %, (−0.6 ± 1.1) %, (0.9 ± 1.4) %, (2.8 ± 1.2) %, and (0.9 ± 2.2) %, respectively. The O2–O2 collision-induced absorption and absorption by methane are obtained with high precision at the 0.8 nm resolution of our BBCES instrument in the 307–725 nm wavelength range. New dispersion relations for N2O, SF6, and CH4 were derived using data in the UV–vis wavelength range. This study provides dispersion relations for refractive indices, n-based Rayleigh scattering cross sections, and absorption cross sections based on more continuous and more extended wavelength ranges than available in the current literature.
Highlights
The dominant interactions of gas-phase molecules with light in Earth’s atmosphere can be divided into absorption, where the light energy is converted to internal energy and generally transferred to the surrounding environment either as heat or as photoemission, and light scattering, where the gases redistribute the light energy in the atmosphere
The light extinction by gases is widely used for determining the effective optical pathlength of high-finesse optical cavities that measure trace gases and aerosols (Washenfelder et al, 2008, 2013; Wilmouth and Sayres, 2019; Jordan et al, 2019) and for differential optical absorption spectroscopy (DOAS) to infer information about the light extinction properties of aerosols and clouds in the open atmosphere (Baidar et al, 2013; Platt and Stutz, 2008)
The reflectivity curve of the BBCESVis is much more structured, with reflectivity ranging between 0.999224 ± 0.000010 and 0.9999550 ± 0.0000006 (776 ± 10 ppm > loss > 45 ± 0.6 ppm) over a wide wavelength range of [338–725] nm
Summary
The dominant interactions of gas-phase molecules with light in Earth’s atmosphere can be divided into absorption, where the light energy is converted to internal energy and generally (at atmospheric pressures) transferred to the surrounding environment either as heat or as photoemission, and light scattering, where the gases redistribute the light energy in the atmosphere. The interaction of light with a wavelength much larger than the size of a molecule/particle gives rise to the scattering of light, which is known as Rayleigh scattering (Strutt, 1899). Rayleigh scattering accounts for scattering, local field effects (Lorentz–Lorenz) (Strutt, 1920), and depolarization from the non-sphericity of molecule/particles (King correction factor) (King and Eve, 1923; Strutt, 1918). For a gas with known refractive index (nν) and King correction factor (Fk(ν)), the wavelength-dependent Rayleigh scattering cross section (σν cm molec.−1) can be calculated as follows
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