California clean air groups aim to reduce smog levels by limiting pollution from lawn mowers.

The state's air pollution control board has passed new regulations limiting emissions from the machines and other small petrol-fuelled machines.

By 2007, the California Air Resources Board has stipulated, all small equipment sold in the state powered by petrol or diesel must be equipped with catalysts, improved carburettors and leak-proof fuel tanks and lines.

The state estimates that the law will add $45 to the price of a lawn mower, at a cost to the industry of $85 million annually.

Emissions would be cut by a third by 2020, it is thought, unless a challenge is successfully mounted to the plan in Congress.