What is the atmospheric composition of venus?

Answer 1

Carbon Dioxide according to Walter Adams and Theardore Dunham.

Answer 2

The atmosphere on Venus is composed mainly of carbon dioxide (96.5%)and nitrogen (3.5%), with less than 1% of other gases: carbon monoxide, argon, sulfur dioxide, and water vapor.

The thick clouds of sulfur dioxide and sulfuric acid trap heat on the planet, creating an average planetwide surface temperature of 460° C (860°F).

More Precisely

Venus's atmosphere consists of Carbon Dioxide (96.5%), Nitrogen (3.5%), Sulfur Dioxide (150 parts per million), Argon (70 ppm), Water Vapor (20 ppm), Carbon Monoxide (17 ppm), Helium (12 ppm), Neon (7 ppm), Hydrogen Chloride (0.1-0.6 ppm), and Hydrogen fluoride (0.001-0.005 ppm). Carbon dioxide makes up 96% of the atmosphere, which has a pressure at the surface of 92 atmospheres, or 0.61 tons per square inch.

The temperature is 400-500 degrees C so the carbon dioxide is near the boderline between being a gas and a supercritical fluid.