Sulfur dioxide in the Venus atmosphere: Distribution and implications

Abstract

The Pioneer Venus Orbiter Ultraviolet Spectrometer sees variable disk brightness features similar to the well‐known "UV markings" seen at longer wavelengths. The bright features are consistent with a homogeneous cloud of H 2 SO 4 aerosols. The darker features show the presence of a broad‐band absorber, which is at some depth in the cloud layer. Additional contrast arises from SO 2 absorption. The observed strength of the SO 2 absorption as a function of wavelength rules out a uniform mixing ratio for the SO 2 . The data are well fitted by an inhomogeneous light scattering model in which the SO 2 scale height is one‐fifth of the CO 2 scale height and the mixing ratio of SO 2 at 40 mb is 1 × 10 −7 . A model of the oxidation of sulfur dioxide in the upper cloud reproduces the observed vertical distribution of SO 2 and indicates that SO 2 alone is sufficient to produce the observed amount of H 2 SO 4 in this region.