The first stage of the programme is due to be completed by May and improvements in regional air quality should start to be seen a few months later, Sarah Liao Sau-tung said in an interview with the South China Morning Post.

And significant improvements should be achieved when the programme is completed by 2007, the secretary for the environment, transport and works said.

Under the programme, the cleaning devices will be installed in power plants in Shajiao, Huangpu, Taishan and Zhuhai in the Pearl River Delta region by 2005.

Similar works will be carried out on all oil-fired and coal-fired power plants with a capacity over 125 megawatts by 2007.

Dr Liao admitted that the region's air quality had deteriorated over the past three years despite stepped up efforts by Hong Kong to cut its air pollutants.

Last year, the number of days when 'very high' ambient pollution levels were recorded leapt to 602 hours from 262 hours in 2002. This was despite a 7 per cent improvement in roadside pollution levels over the same period.

The poor ambient air quality is mainly attributed to power plant emissions as the region races to meet surging demand for electricity amid its fast economic growth.

'Some of the small power plants that were previously shut down have been reopened as Guangdong suffers from a power shortage,' Dr Liao said.

The province has a policy to close down plants with a generation capacity below 50 megawatts as they are old and use polluting fuel. It also aims to phase out all power plants smaller than 300 megawatts in capacity by 2005.

There are at least 90 power plants in the Pearl River Delta region and some of largest plants are close to Hong Kong.

Humen has three coal-fired power plants with a combined capacity of 4,000 megawatts, the biggest in the province and equal to the capacity of CLP Power's Castle Peak plant.

The Humen power plants, which are close to thousands of factories owned by Hong Kong businesspeople in Dongguan, were identified as one of the key pollution sources by a regional air quality study commissioned by Guangdong and Hong Kong authorities two years ago.

The study found that Guangdong generated 80 per cent of the air pollution in the Pearl River Delta region, while Hong Kong accounted for the remaining 20 per cent.

In the longer term, Dr Liao hopes a cross-border emission trading scheme can be set up to assist other power plants in Guangdong to cut emissions in a more cost-effective manner.

In the meantime, the government has started talks with CLP Power and Hongkong Electric on emission reduction and an emission trading scheme.

This is the second of a three-part series in which Sarah Liao discusses environmental issues.

Next: conservation