The Ministry of Environmental Protection will keep a close watch for the possible return of energy-intensive and heavy-polluting firms during the stimulus drive, as the environment improved a lot last year, its minister said yesterday.

Zhou Shengxian, minister of environmental protection said at a national conference on environmental protection that the ministry will keep a close check for such projects.

The government announced a 4 trillion yuan ($586 billion) stimulus package in November, and is considering more measures to boost the economy amid the financial crisis.

Zhou said yesterday that factories with backward facilities "would revive", using the excuse of the country's massive investment plan to boost domestic demand.

The country should also be alert to the risk of increased pollution during the economic downturn, as firms running at a loss could suspend the operation of pollution-treatment facilities to reduce costs, Zhou said.

"All these will ruin the country's achievements made on pollution reduction," he said.

Preliminary ministry statistics show that last year, China's emissions of sulfur dioxide and the chemical oxygen demand both fell.

The country's 11th Five-Year Plan (2006-10) requires that by 2010, emissions of sulfur dioxide should be down 10 percent from the 2005 level.

China needs to "sprint" this year to achieve its green goals, Zhou said.

The China Environmental Monitoring Center also said yesterday that 113 major Chinese cities enjoyed 90 percent good air quality last year, up 1.8 percent from 2007.

Water quality at 746 monitoring stations nationwide also showed improvement. The proportion of water-quality level I-III, regarded as good quality, reached 47 percent last year, up 4 percent year-on-year.

"Factory closures due to the economic slowdown are not the only factors that aided the better performance. The Green GDP concept and the government's long-standing environmental protection measures also helped," said Xia Yeliang, an economist at Peking University.

Wu Changhua, greater China director of the London-based Climate Group said last year saw fewer emissions as most of manufacturers reduced production in the wake of fewer orders.

More visible impacts on the environment are expected this year as the economic slowdown usually has a sluggish effect, said Zhang Jianyu, head of the US-based Environmental Defense Fund's China office.

"In the past, coal-fired power plants accounted for 60 percent of pollutants and emissions, but the new focus on alternative energy will help reduce pollution levels," said Qi Ye, an environmental professor at Tsinghua University.