ATMOS

The Atmospheric Omission System (often referred to as ATMOS) was a device created by the Sontarans in the 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 at the dashboard which could not be disabled and when activated ATMOS was programed to contradict drivers' orders.

There were 17 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 guise that ATMOS was his own invention even though it was decades ahead of Earth technology of the time. All cars in Britain were fitted with them and after going worldwide ATMOS existed in 400,000,000 cars.

When it first came onto the market UNIT suspected ATMOS might be alien, but their investigations turned up nothing until 52 simultaneous deaths occurred involving ATMOS-fitted cars. They called the Doctor and it was discovered that their ulterior usage was that 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 was disabled when the Sontarans were defeated.(DW: The Sontaran Stratagem / The Poison Sky)

Behind The Scenes
ATMOS is a major plot element of The Sontaran Stratagem / The Poison Sky. However, the word "ATMOS" first appeared on a taxi in Partners in Crime.

Naming
As ATMOS meant Atmospheric Omission System, when the Doctor called it ATMOS system, he was officially incorrect, as then it would be Atmospheric Omission System system, which is a tautology.