The Poison Sky

Four hundred million cars on Earth equipped with ATMOS devices are suffocating humanity with poisonous gas.

Following UNIT's offensive, the Doctor ventures into the factory and discovers the real Martha in one of the Sontarans' cloning devices.

Humbled, Rattigan reactivates the teleport and switches places with the Doctor, sacrificing himself to activate the device and destroy the Sontarans.

The Valiant is equipped with a version of the Torchwood weapon that destroyed the Sycorax ship in "The Christmas Invasion".

to Colonel Mace while they are wearing gas masks, in reference to the events of "The Empty Child"/"The Doctor Dances".

[3] When the Doctor interrupts the Sontarans' transmission, animated footage from CBeebies's part live action, part animation[4] eco adventure show Tommy Zoom is brought up on screen featuring the villainous Polluto disguised as a magician and the heroic Tommy and his dog Daniel as his audience.

[2] As in many previous episodes of the revived series, supposed BBC News 24 footage is used featuring reports of unfolding events.

However, as with the more recent appearances of such footage in Doctor Who, the channel is simply captioned on screen as 'News 24' devoid of the BBC logo.

[8] During production, director Douglas Mackinnon intended to have the episode's climactic scene in the TARDIS show the moveable column in the centre console move up and down much more rapidly than normal.

[10][11] Unofficial overnight figures indicated that "The Poison Sky" was watched by 5.9 million viewers, giving it a 32.5% share of the total television audience.