When it comes to air pollution, the long-suffering residents of Beijing tend to think they have seen it all. But this weekend, instruments measuring the levels of particulate matter in the city’s famously noxious air broke all records.

The Beijing Municipal Environmental Monitoring Centre said levels of PM2.5, tiny particulate matter, had reached more than 600 micrograms per square metre in many areas, and Reuters said it may even have hit 900 – its worst-ever reading.

The World Health Organisation considers a safe daily level to be 25.

The artist Ai Weiwei offered his own succinct commentary on the city’s atmospheric conditions by donning a gas mask in a photograph he posted on Twitter, his salt-and-pepper beard and tufts of hair sticking out around the device amid the smog.

Children and the elderly were urged to stay indoors and some residents who ventured out wore face masks as the acrid murk entered its third day.

Air quality has long been a problem in the Chinese capital, but this weekend saw levels more than 30 times above the level judged safe by the World Health Organisation.

Breakneck economic growth, reliance on coal, dramatic expansion of car ownership and the widespread flouting of environmental laws have all contributed to China’s air pollution problems. But the intensity of the current problem appears to be weather-related. The monitoring centre said the heavy pollution had been trapped by an area of low pressure and warned that the problem was likely to continue until Tuesday.

It also urged people to avoid outdoor activities and said children and elderly people should not venture outdoors. Beijing began publishing PM2.5 readings early last year.

via Top tip if you’re going out in Beijing: don’t breathe | World news | The Guardian.