Atmosphere

An atmosphere was a gaseous envelope surrounding planets, such as Earth.

Space had no atmosphere, so people needed to wear spacesuits when in outer space. (TV: Enlightenment)

Earth
Earth, and later on, the terraformed Mars' atmosphere, was 80% nitrogen and 20% oxygen. (AUDIO: The Resurrection of Mars) New Earth had the same atmosphere as Earth, which was why humans made it their new home after Earth was destroyed. (TV: New Earth)

According to Rose Tyler, cows farting methane into the atmosphere was one of the causes of global warming on Earth. (AUDIO: The Flood)

Due to human activity, Earth had a lot of toxins and dioxins in its atmosphere, which would have provided decent nutrition for the Nestene Consciousness. (TV: Rose)

During the Year That Never Was, Earth's atmosphere was temporarily opened to unleash an army of Toclafane. (TV: The Sound of Drums)

In 2009, 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. (TV: The Poison Sky)

In a parallel world, Earth's atmosphere was poisoned by the Sontarans and then cleared by Torchwood Three. (TV: Turn Left)

By the 2020s, the amount of carbon in Earth's atmosphere was dangerously high. (AUDIO: A Postcard from Mr Colchester)

In a possible future, Earth became an orphan planet called Orphan 55, which had an atmosphere made of carbon dioxide. The Dregs adapted to breathe it. (TV: Orphan 55)

Earth's atmosphere was contaminated after the fall of Satellite Five. (TV: Bad Wolf)

Atmospheres of other worlds
The atmosphere of the planet Mars began to thin "many millions of years" before the 23rd century. (AUDIO: Deimos) This allowed ultraviolet radiation to reach the surface, poisoning the Ice Warriors who lived there. (AUDIO: Red Dawn, The Judgement of Isskar) By 1881, Mars' atmosphere had "all but evaporated", (TV: Empress of Mars) requiring anyone on the surface to wear a spacesuit to survive the poor atmosphere. (TV: The Waters of Mars) In the 23rd century, the Eighth Doctor helped terraform Mars into a suitable human colony, giving it the same atmospheric composition as Earth. (AUDIO: The Resurrection of Mars)

Alfava Metraxis had a breathable atmosphere. (TV: The Time of Angels)

Elliot Sardick was able to control the atmosphere of his home planet, allowing him to release the sky fish that resided there into the air beneath at his discretion. (TV: A Christmas Carol)

The planet Malcassairo had an atmospheric shell. (TV: Utopia)

During the Thousand Year War, the detonation of various nuclear and chemical weapons had poisoned Skaro's atmosphere. (TV: Genesis of the Daleks) After the early Daleks had ended the fighting by detonating a neutron bomb, (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe) Skaro's atmosphere became so irradiated that nothing could survive the outside world without survival equipment. After five centuries, the radiation levels began to drop but the Daleks, discovering that they had adapted to survive on radiation, sought to flood their nuclear waste into the atmosphere but were defeated by the Thals in the Thal-Dalek battle. (TV: The Daleks) Held in suspended animation in the city's secret incubation level, the Dalek Supreme, after having overcome the dependancy on radiation, provided the Thal Tryana with the blueprints for a network of ionising towers that reduced the radiation present in Skaro's atmosphere. Fifty cycles after the battle, the atmosphere, while still having a higher than normal level of radioactivity, was safe to exist in without the anti-radiation drug. (AUDIO: Return to Skaro) During the era of the New Dalek Paradigm, Skaro's atmosphere had healed to be in a state similar to Earth's, though it was plagued by sulphuric rain. (GAME: City of the Daleks, TV: Asylum of the Daleks)

At the Fall of Gallifrey, the Doctor's first life cycle flew their TARDISes into Gallifrey's lower atmosphere so that they could shunt the planet into a pocket universe. (TV: The Day of the Doctor)

The Scabus came from a planet whose atmosphere was once rich in carbon dioxide before a more advanced species colonised the planet and altered the atmosphere to do so, drastically reducing the carbon dioxide present. (AUDIO: Terror of the Master)

During the 2400s Dalek invasion of the solar system, Venus had a humid atmosphere, the invading Daleks having to coat themselves with lead to prevent their casings from rusting. (PROSE: Red for Danger)

Other references
"[They] who said the verse made the atmosphere worse" was a saying associated with farting. (TV: From Raxacoricofallapatorius with Love)