Atmosphere of Venus
The atmosphere of Venus is the layer of gases surrounding Venus. It is composed primarily of carbon dioxide and is much denser and hotter than that of Earth. The temperature at the surface is 740 K (467 °C, 872 °F), and the pressure is 93 bar (9.3 MPa), roughly the pressure found underwater on Earth. The Venusian atmosphere supports opaque clouds made of sulfuric acid, making optical Earth-based and orbital observation of the surface impossible. Information about the topography has been obtained exclusively by radar imaging. Aside from carbon dioxide, the other main component is nitrogen. Other chemical compounds are present only in trace amounts.
Chemical cycling
The majority of known chemical cycles on Venus involve its dense atmosphere and compounds of carbon and sulphur, the most significant being a strong carbon dioxide cycle. The lack of a complete carbon cycle including a geochemical carbon cycle, for example, is thought to be a cause of its runaway greenhouse effect, due to the lack of a substantial carbon sink. Sulphur cycles including sulphur oxide cycles also occur, sulphur oxide in the upper atmosphere and results in the presence of sulfuric acid in turn returns to oxides through photolysis. Indications also suggest an ozone cycle on Venus similar to that of Earth's.