More dangerous pollution in Beijing

Days after record air pollution caused an outcry in Beijing, smog in the capital on Wednesday (January 23) shot back up to levels considered 'hazardous,' highlighting the long-term environmental challenge facing authorities.

Beijing's official air quality monitoring system showed pollution hovering between 300 and 400 on an index that measures particulate matter in the air with a diameter of 2.5 micrometers, known as PM2.5.

The U.S. embassy in the Chinese capital measured an index of 435 at 11am (0300gmt) on Wednesday.

A level of 300 is considered dangerous while the World Health Organisation recommends a daily level of no more than 20.

On January 12, levels exceeded 700, increasing the number of patients visiting the city's hospitals with respiratory complaints.

Emissions from factories and heating plants, fumes from millions of vehicles and the burning of coal bricks to heat homes often conspire to blanket the city in a pungent haze that can become trapped when weather conditions are right.

A thick, grey mist hung over the metropolis of 20 million people on Wednesday, obscuring the red-tiled rooftops of the Forbidden City at its centre.

Smog also covered the Beijing's suburbs on Wednesday, and visibility was low at Beijing's Capital International airport.

Around ten percent of flights were delayed in the early morning, the airport's hotline told Reuters, but most flights were leaving on time by the early afternoon.