The New York Times reported that Volvo is experimenting with a system that will take car interior air filtering to a level above common dust filters and the fume filters found in certain car models. The paper said the Volvo air-filtration system, not only cleans the cabin air better than any other car's does now, even in the confines of a tunnel, but works with the car turned off. It is also self-purging, which means that unlike conventional filtration systems, it does not need regular maintenance. The New York Times said, using a technology common to military gas masks, its filters collect molecules of hydrocarbons and nitrous oxides. Roughly every two days the filters are heated and the trapped gases released into the engine's emission control catalyst, where pollutants are transformed into water vapour, nitrogen and carbon dioxide. The paper said that, in a polluted environment like a parking garage, a fan quietly activates the system, leaving the air in the whole place a tiny bit cleaner while the driver is not even there. The technology is so new that instrument panels would have to be reworked to include it, so Volvo does not expect to make it available until its next major model change a few years from now.