The air in much of China is so bad the government has repeatedly declared "war" on it. The enemy are tiny particulates which spew forth from countless cars, coal-fired power stations and steel plants to create a dense, putty-coloured smog. Known as PM2.5s, after their length in micrometres, the particulates contain toxic droplets so small they embed deep in the lungs and sometimes even the bloodstream. A former Chinese minister of health has estimated that as many as 500,000 Chinese citizens die prematurely because of them every year. Others have suggested the figure is far higher. Campaigners speak of an ‘airpocalypse’.