Washington state officials have approved legislation adopting California’s tougher emission standards.

Signed by Washington governor Christine Gregoire on May 6th, the legislation includes future caps on greenhouse gas emissions and aims to produce cleaner air and reduce gasoline use by requiring that cars and light trucks sold in the state in the future meet stricter auto exhaust standards.

"Motor vehicles are the largest source of air pollution in our state," Ms Gregoire explained. "With this legislation, we are taking a significant step in reducing pollution, and we will gain the added benefit of promoting fuel-efficient vehicles that save money for consumers at the gas pump."

The current Californian low-emission vehicle standards require that new cars sold in the state reduce emissions of nitrogen oxides and hydrocarbons beyond federal standards.

Eight other states have now adopted the California standards, which also include plans to phase in caps on greenhouse gas emissions beginning with the 2009 model year.

Cars sold in Washington would not have to comply with California standards until at least the 2009 model year and the actual timing depends on when Oregon adopts the standards.

The new emissions standards will start taking effect in 2009, and by 2016 all new cars, SUVs and light trucks sold in Washington will have to comply. California estimates that the new regulations will reduce emissions in cars and light trucks by 25 per cent and in larger trucks and SUVs by 18 per cent.

Diesel cars use platinum catalysts to control harmful exhaust emissions.