It will take at least 10 years to improve air quality in the Pearl River Delta, even if an emissions trading scheme is implemented, the environment chief said yesterday. Secretary for Environment, Transport and Works Sarah Liao Sau-tung said she was confident emissions trading schemes could bring tremendous benefits. Under the schemes, companies that produce fewer emissions than permitted can save their emissions points for future use or trade them with firms that cannot meet pollution targets. Dr Liao is pushing for a cross-boundary trading scheme with Guangdong and Macau. 'We wish we had a magic wand to clean up the air. Whatever we do, we are talking about a number of years - say 10 years, that sort of time frame,' she said at a forum on emissions trading at the Open University in Ho Man Tin. Dr Liao said a successful scheme could eventually lead to an emissions exchange as part of the Hong Kong stock exchange, while the world eyed the mainland's huge emissions trading market. Professor Peter Hills, of the University of Hong Kong's Urban Planning Centre, urged the government to move quickly to investigate such a scheme. 'We just can't sit and discuss things endlessly. It is just like the switch to cleaner fuel. It took us 10 years to do it,' he said. But Anne Smith, vice-president of Charles River Associates business consultants in Washington, sounded a note of caution. 'As to how to achieve emission reductions, we should not be locking on to emission trading as there are other mechanisms out there which could provide flexibility to meet the target,' she said.