Beijing will not only have to reduce existing pollution in the city over the next five years, but also control any potential increases in pollution, an environmental official said Thursday.

As Beijing's population, energy consumption and urban expansion continue to increase, so must the city's vigilance over pollution, said Du Shaozhong, deputy chief of the Beijing Municipal Environmental Protection Bureau.

According to the 2010 Beijing Municipal Environmental Status Report, the city's average density of sulfur dioxide fell to 0.032 mg per square cubic meter last year, a 12-year record low.

Emissions of sulfur dioxide were reduced by a little more than 3 percent year-on-year in 2010, dropping to 115,100 metric tons, the report said.

The improvements in Beijing's air quality were hard-earned, as Beijing's gross domestic product (GDP) increased by 10.2 percent last year, Du said. An increase in the number of automobiles in the city also made it hard to reduce pollution, Du said.

Beijing had nearly 4.8 million registered automobiles by the end of last year, according to the report.

Last year, the city eliminated more than 50,000 vehicles that did not meet emission standards, as well as shut down cement plants and lime kilns that were under capacity, in order to reduce pollution, Du said.