Beijing has taken a tougher stance on polluters in the first four months of the year with total fines exceeding 20 million yuan, a municipal environmental watchdog said on Wednesday.

Up until the end of April, the capital has filed 2,113 cases with environmental pollution totaling 20.9 million yuan in fines, among which 55 percent came from companies discharging air pollutants, said the Beijing Municipal Environmental Protection Bureau on Wednesday.

In addition, 11.2 percent of the fines were from polluters who polluted the water resulting in about 2.18 million yuan worth of fines in the first four months, the bureau said.

In March, the capital has launched an annual campaign aiming to control the air pollution, among the series of efforts, the tougher reins targeted on companies has been treated as a major tool.

"The strengthened controls on companies have worked. In the first four months, the capital has seen the PM2.5 concentration – particulate matter with diameter less than 2.5 microns that hazardous to human health – reducing it by 21.8 percent year-on-year," the bureau said.

In April, the concentration of PM2.5 was lowered to 67.8 microgram per cubic meter.

Days with good air quality have increased by 20 days compared to the amount in the first four months of last year.