Atmosphere

An atmosphere was a gaseous envelope surrounding planets, such as Earth.
 * Earth's atmosphere consisted of 78.08% Nitrogen, 20.94% Oxygen, 0.93% Argon and 0.042% various other elements and compounds.
 * The Doctor often checked that the planets he visited had a breathable atmosphere before leaving the TARDIS.
 * Space had no atmosphere, so people needed to wear spacesuits when in outer space. (DW: Enlightenment)
 * Earth had a lot of toxins and dioxins in its atmosphere, which would have provided decent nutrition for the Nestene Consciousness. (DW: Rose)
 * Earth's atmosphere had been contaminated after the fall of Satellite Five. (DW: Bad Wolf)
 * New Earth had the same atmosphere as Earth, its predecessor. (DW: New Earth)
 * The planet Malcassairo had an atmospheric shell. (DW: Utopia)
 * Earth's atmosphere was temporarily opened to unleash an army of Toclafane. (DW: The Sound of Drums)
 * The Tenth Sontaran Battle Fleet made Luke Rattigan develop the ATMOS in cars across the entire planet Earth. This was part of their plan to poison Earth's atmosphere with Clone Feed, so Earth could become the new clone world for the Sontaran species. The Tenth Doctor later cleared the atmosphere, saving the planet. (DW: The Poison Sky)
 * In an alternate timeline, Earth's atmosphere was poisoned by the Sontarans and then cleared by Torchwood Three. (DW: Turn Left)
 * The Tenth Doctor needed a spacesuit on Mars as it had a poor atmosphere. (DW: The Waters of Mars)
 * Alfava Metraxis had a breathable atmosphere. (DW: Time of Angels)