ATMOS

The Atmospheric Omission System (often referred to as ATMOS) was a device created by the Sontarans for their plan to convert Earth in 2009. ATMOS devices, able to reduce carbon dioxide emmissions 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 ignore drivers' orders.

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)

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 was a tautology; Luke Rattigan pedantically reminded them of this. (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.
 * The system's full name appears to be an incorrect usage of "omission", which means the act of leaving something out. One would expect the word to be its homophone "emission", referring to gases emitted from the car's engine.