A green group has accused the government of dodging its duty to clear the city's polluted air by adopting less stringent targets meant for use by developing countries. Chief Executive Donald Tsang Yam-kuen has said the government would consider replacing the city's 21-year-old air-quality objective with the World Health Organisation's 'interim target-1' standard, which measures particulate matter. Friends of the Earth noted yesterday that it was the lowest standard among the four listed by the WHO for countries at different stages of development. Countries are expected to abide by stricter standards as they move up the stages. As a 'world-class city', Hong Kong should not be bound by the lax targets designed for developing countries, the group said. In response, the government said it was still reviewing its air-quality guidelines, and noted that in adopting the interim targets, the WHO had left it to individual countries to adopt what suited them best. Meanwhile, hundreds of buildings in the city, including the Convention and Exhibition Centre and the Peak Tower, will go dark for an hour on March 28 to join the WWF's 'Earth Hour' global campaign that rallies people to save energy. Trevor Yang Chi-hsin, chairman of WWF Hong Kong, said the government and more than 140 business and community groups would take part.