ATMOS

ATMOS, short for Atmospheric Omission System, was a device created by the Sontarans for their plan to convert Earth into a Sontaran hatchery in 2009. ATMOS devices, able to reduce carbon dioxide emissions to zero, could be threaded through every make of car and included a computer system with integrated GPS navigation on the dashboard which could not be disabled. When activated, ATMOS was programmed to completely contradict drivers' orders; this could be used against it as demonstrated by the Tenth Doctor who ordered it to drive into a river, prompting it to immediately stop. It tended to ominously sign off with the words "This is your final destination".

There were seventeen factories worldwide, though the ATMOS factory in London served as a central depot. ATMOS devices were sold to humans by Luke Rattigan's company under the claim that ATMOS was his own invention even though it was decades ahead of Earth technology of the time. Almost all cars in Britain were fitted with them and after going worldwide ATMOS existed in four hundred million cars.

When it first came onto the market, UNIT suspected ATMOS might be alien, but their investigations turned up nothing until fifty-two simultaneous deaths occurred involving ATMOS-fitted cars. They called the Tenth Doctor and it was discovered the Sontarans intended to use the cars as weapons to release clone feed into the atmosphere and convert Earth into a cloning world. All ATMOS were disabled when the Sontarans were defeated. (TV: The Sontaran Stratagem / The Poison Sky)

Parallel world
In a parallel world, ATMOS also affected the whole world. A soldier shot at his ATMOS-fitted car, which continued to release gas even after switching it off. Rose Tyler told Donna Noble that because of Britain's lack of petrol, it wasn't as bad as in other countries that were being choked by the gas. Gwen Cooper and Ianto Jones gave their lives to stop ATMOS, while Captain Jack Harkness was transported to the Sontaran homeworld. (TV: Turn Left)

Naming
As ATMOS was an abbreviation of "Atmospheric Omission System". When the Doctor and General Staal called it "ATMOS system", they were technically incorrect, as then it would be "Atmospheric Omission System system", which, as Luke Rattigan pedantically reminded them, was a tautology. (TV: The Sontaran Stratagem / The Poison Sky)

Behind the scenes

 * ATMOS was a major plot element of The Sontaran Stratagem / The Poison Sky. However, the word "ATMOS" first appeared on a taxi in Partners in Crime. It is mentioned that at the time of the events of The Sontaran Stratagem ATMOS had existed for some time. When the Doctor asked what it was, Donna, his companion, responded that it had been around for so long even she knew what it was.