Evidence for an Elemental Sulfur Component of the Clouds from Venus Spectrophotometry

Abstract

The decrease in the reflectivity of Venus in the near UV can be explained if the clouds contain particles of elemental sulfur in addition to sulfuric acid. The low-resolution McDonald-Pittsburgh spectrum can be fitted by two sulfur-containing, multiple-scattering cloud models: 1) a mixed cloud consisting of one particle of elemental sulfur of radius 10 µm for every 670 particles of sulfuric acid of radius 1 µm, and 2) a layered cloud of optical thickness τ = 1.0 consisting of 1 µm particles of sulfuric acid overlying a thick cloud of elemental sulfur particles of radius 3.6 µm: Some of the sulfur is incompletely polymerized. The source of the sulfur is photo-dissociation of COS, although some may also be recycled from the lower atmosphere. The sulfur plays a crucial role in the planetary meteorology of Venus since it is responsible for the bulk of the absorption of solar energy.