According to the capital's plan to limit coal consumption, all coal-fired boilers in the downtown area will be replaced with natural gas burners by the end of 2014.

Since 2001, when the capital initiated its coal reduction project, there has been a sharp drop in the amount of sulfur dioxide in the city's atmosphere, according to the bureau. In 1998, there was 120 micrograms of sulfur dioxide per cubic meter; this year, it was cut to 28 micrograms per cubic meter.

The capital aims to replace large-scale coal-fired boilers in its suburban areas by the end of 2017.

Liu admitted on Wednesday that there is a long way to go before capital residents see smog-free winters.

"To replace coal with natural gas for heating and power will cut down on the intensity of sulfur dioxide, smoke and dust in the air, but it won't necessarily mean we'll have a smog-free winter. The capital has various sources of pollution and coal is only a part of it," Liu said.

Responding to questions about Beijing's lack of natural gas, Liu said the capital has a sufficient supply of natural gas for the coming winter.

The city buys its natural gas from the Inner Mongolia autonomous region, the Xinjiang Uygur autonomous region, and Shaanxi and Hebei provinces.