BEIJING, (Xinhua) -- Air pollution, especially acid rain, has posed great challenge to the smooth achievement of China's big goal of building a fully well-off society, China's national environmental watchdog Thursday said Thursday at a press conference.

The degree of acid rain contamination had climbed up in 2005 but the area basically remained stable, said the State Environmental Protection Administration (SEPA).

A SEPA list finds 357, or 51.3 percent, of all the 696 cities and counties that carry out acid rain monitoring across the country had experienced the rain.