As world leaders gather in Paris for climate change talks, Sky News's Katie Stallard was reporting from Beijing, where smog is almost 20 times higher than safe levels determined by the World Health Organisation.
It looks, I am very aware, quite ridiculous, but the air here is so bad today, we're being given advice from the ministry of environmental protection that people should be staying inside, that if you are outside you should be wearing a mask.
Stallard's air quality iPhone app was indicating air pollutant per cubic meter of air (µg/m3) as almost 600. The WHO's safe level is 25µg/m3. She later demonstrated that being inside was also hazardous.
China emits more carbon than any other nation, and according to the country's ministry of environmental protection, the haze over northern China is now 530,000 square kilometres big. As Quartz notes, that's equivalent in size to Spain or California.
Leaders from 147 nations and negotiators from 195 countries are in Paris for the United Nations climate change conference known as COP21.