Beijing's skies have been covered with a toxic cloud for nearly a week, and Li Keqiang, the No. 2 leader in China's Communist Party, asked the city's residents to be patient during the long-term cleanup.

Lower-level officials took steps to reduce traffic and factory emissions to clear the worst outbreak of smog on record. But that move is likely to produce only short-term relief from a chronic problem.

"It is really just a temporary measure, and in the longer term you really have to get at the root causes like coal-burning factories," said Ming Sung, chief Asia-Pacific representative with the U.S.-based Clean Air Task Force.

Environmentalists and analysts credit the problem to a complex mix of causes, including overreliance on industry, dependence on coal, poor enforcement of pollution laws, and incentives for local officials to promote economic growth above all else (David Stanway, Reuters, Jan. 17). -- KJ