BEIJING, Dec. 30 -- Industrial pollution is the biggest source of the PM 2.5 problems which cause Beijing's smog, the Chinese Academy of Sciences said on Monday.

Secondary inorganic aerosols -- sulfates and nitrates -- are responsible for 26 percent of Beijing's PM 2.5, followed by industrial production and coal burning at 25 percent and 18 percent. Soil dust accounted for 15 percent. Beijing's heavily industrialized neighboring provinces add to pollution in the capital.

The report suggests that energy structure improvement and regional cooperation are needed to combat air pollution.

Days of smog over large parts of China caused traffic jams and school closures earlier this month.

Scientists sampled PM 2.5 in different seasons and analyzed its chemical composition and seasonal variation from 2009 to 2010. The research findings were published in the influential "Atmospheric Chemistry and Physics".