Laboratory measurement of the temperature dependence of gaseous sulfur dioxide (SO₂) microwave absorption with application to the Venus atmosphere

Abstract

High‐accuracy laboratory measurements of the temperature dependence of the opacity from gaseous sulfur dioxide (SO 2 ) in a carbon dioxide (CO 2 ) atmosphere at temperatures from 290 to 505 K and at pressures from 1 to 4 atm have been conducted at frequencies of 2.25 GHz (13.3 cm), 8.5 GHz (3.5 cm), and 21.7 GHz (1.4 cm). Based on these absorptivity measurements, a Ben‐Reuven (BR) line shape model has been developed that provides a more accurate characterization of the microwave absorption of gaseous SO 2 in the Venus atmosphere as compared with other formalisms. The developed BR formalism is incorporated into a radiative transfer model. The resulting microwave emission spectrum of Venus is then used to set an upper limit on the disk‐averaged abundance of gaseous SO 2 below the main cloud layer. It is found that gaseous SO 2 has an upper limit of 150 ppm, which compares well with previous spacecraft in situ measurements and Earth‐based radio astronomical observations.