Volvo has made large efforts to reduce its environmental impact. Beginning at the manufacturing stage, Volvo claims to have reduced solvent emissions from 30kg per car in 1977 to 1.3kg per car in 2004. In 1991 it created a database of all chemicals used in its factories and has been working since then to reduce or eliminate all the harmful ones. Volvo also recycles water used in the factory to ensure that waste water containing harmful chemicals is not released. Volvo’s PremAir system coats the car radiator with chemicals that neutralise oxides of nitrogen and low-level ozone. Volvo also offers cars in the US with a Partial Zero Emission engine – when the car is warming up the PZEV engine will run a very lean mix of petrol and air to reduce emissions and reduce warm-up time. Volvo has started to introduce models of its cars which run on bi-fuel – allowing a car to be topped up with petrol and Compressed Natural Gas (CNG). Since the CNG comes from bio-methane, carbon dioxide emissions are virtually zero. Future efforts include the forthcoming VVC (Volvo Versatility Concept) which sports an auto-off idling function when stationary in traffic; compression auto ignition which means that at low speeds the engine runs without a spark plug, reduces carbon dioxide emissions and does so without the other emissions associated with diesel engines.