With only 11 days to go until the start of the Beijing Olympics, this was the smoggy scene in the Chinese capital yesterday.

Visibility was down to half a mile in some parts, including the National Stadium, while the Athletes' Village complex could not be seen from the nearby Olympic Green.

The city's notoriously polluted air has cast a cloud over the Games, with organisers threatening to postpone events if it is bad.

Today state media reported drastic measures - pulling more cars from the roads and shuting down additional factories - could be taken if the air quality does not improve.

'The air quality in August will be good,' Du Shaozhong, deputy director of the Beijing Municipal Environmental Protection Bureau, told reporters on Sunday. He did not explain the reasons for his optimism.

Wind can blow pollution to Beijing from thousands of miles (kilometers) away, while a lack of wind can cause chemicals and particulate matter to build up in the city.

'There's only so much you can do with local emission reduction,' said Veerabhadran Ramanathan, an atmospheric scientist at the Scripps Institution of Oceanography at the University of California San Diego.

He is leading a team that is studying the impact of Beijing's pollution reduction measures.

'You're basically at the mercy of the winds,' he said.