Photo taken on December 10, 2008 shows the snow-covered Mutianyu section of the Great Wall located on the outskirts of Beijing, capital of China. The first snow of this winter fell in Beijing on Wednesday. [Xinhua]

An API of 51 to 100 indicates fairly good air quality, the China Environmental Monitoring Center said.

An index of 101 to 150 means slight pollution, while an API in excess of 200 means severe air pollution.

Beijing commuters should make more use of public transport to reduce emissions, she said.

On Jan 1, new measures will be introduced to move coal-burning industries out of the city. "They will be replaced with ones that use gas to help reduce pollution," Li said.

On Tuesday, Beijing experienced one of its most polluted days, with the index hitting 247 citywide and 399 in the southern outskirts.