The atmosphere of Venus is composed mainly of carbon dioxide, along with a small amount of nitrogen and other trace elements. The amount of nitrogen in the atmosphere is relatively small compared to the amount of carbon dioxide, but as the atmosphere is so much thicker than that on Earth, its total nitrogen content is roughly four times higher than Earth's, even though on Earth nitrogen makes up about 78% of the atmosphere.
The atmosphere contains a range of interesting compounds in small quantities, including some based on hydrogen, such as hydrogen chloride (HCl) and hydrogen fluoride (HF). There are carbon monoxide, water vapour and molecular oxygen as well. Hydrogen is in relatively short supply in the Venusian atmosphere. A large amount of the planet's hydrogen is theorised to have been lost to space, with the remainder being mostly bound up in sulfuric acid (H2SO4) and hydrogen sulfide (H2S). The loss of significant amounts of hydrogen is proved by a very high D/H ratio measured in the Venusian atmosphere. The ratio is about 0.025, which is much higher than the terrestrial value of 1.6×10−4. In addition, in the upper atmosphere of Venus D/H ratio is 1.5 higher than in the bulk atmosphere