BEIJING, March 1 -- Beijing has launched a "zero-hour" campaign for enforcing the city's first air pollution prevention regulation, which came into effect on Saturday.

Over 400 environmental monitoring staff began work at 12 a.m. Saturday to conduct a scrutiny on industrial emissions and dust.

Among the 617 plants and firms inspected, 25 received fines for discharging excessive emissions and 11 others for improper treatment of dust.

When inspectors arrived at the Hongxiang Heat Co. Ltd. in Changping District, they found emission from roaring coal-fired heating boilers were discharging sulfur dioxide with a density of 350 milligrams per cubic meter, which is seven times more than the city's permitted level.

Zhong Chonglei, captain of the municipal environmental inspection team, said according to the regulation, the company should be given a fine of between 80,000 yuan (13,018 U.S. dollars) and 100,000 yuan. The fine will be doubled if the company fails a further check in a month.

Beijing's local law on air pollution prevention is widely regarded as a test of the government's resolve to solve air pollution problems. It legislates penalties from hefty fines to imprisonment for polluters, and, for the first time, sets a ceiling on total emissions of major pollutants. A previous guideline targeted only growth of emissions.

People in Beijing have just suffered one of the worst weeks of smog ever, only dispersed by a cold front which arrived on Wednesday evening.

Wang Yuesi, a researcher with the Chinese Academy of Sciences (CAS) Institute of Atmospheric Physics, said on Saturday that the dust and haze in Beijing's air were mainly formed by emissions from coal-burning from the metropolitan's nearest regions, which was aggravated by local car exhaust.

Wang delivered his report on the smog monitoring at the CAS's forum in Beijing on Saturday.

He has monitored that during February's smog, the density of sulfate in the air has decreased from the levels recorded before, but the density of nitrate has increased fast.

This means that for better air, thermal power plants should step up denitration work. The pollutant also exists in emission from steel, cement, glass and chemical plants, he said.