Beijing residents have been warned to don air masks and offices and homes to put electric air purifiers on overdrive after air pollution readings soared.

Air pollution readings on Thursday registered more than 20 times the recommended exposure levels by the World Health Organization (WHO).

Beijing Municipal Environmental Protection Bureau readings for PM 2.5 – air particulate smaller than 2.5 microns blamed for a range of severe respiratory ailments – registered over 500 micrograms per cubic meter. The WHO recommends no more than 25 micrograms per cubic meter.

Officials in Beijing issued a severe air warning and urged residents to wear protective masks while outdoors, and said the elderly and schoolchildren should stay indoors until conditions improved.

Beijing residents have been warned to don air masks and offices and homes to put electric air purifiers on overdrive after air pollution readings soared

The winter months in the north of the country tend to be periods of extended bad air pollution. Biting cold forces the region’s coal-burning power plants to meet heating demands, while increased car usage and relentless construction chokes the skies with dangerous particulate.

Beijing’s topography – with hills surrounding much of this city of 20 million people – can also keep the capital immersed in dirty air unless strong winds blow it out.

Certain at-risk residents who find themselves exposed to the bad air over extended periods of time complain of watery eyes, difficulty breathing or other respiratory issues. Long-term exposure can lead to asthma, heart disease and cancer. Prolonged exposure to PM2.5 has also been tied to knocking years off people’s life expectancy.

Despite ideal conditions for poor air quality, the air warning issued Friday was just the first of 2014.

China’s cities are frequently blanketed by pollution caused by coal-burning power plants, factories, and millions of vehicles on the roads.

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