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’. Public anger is rising, and winning this war has become a top priority for the Communist Party. Beijing recently issued its first pollution 'red alert', closing schools, factories and construction sites. It ordered half of all private cars off the road. But such draconian measures were only temporary. The real question, in a country where millions of people still look to industrialisation to lift them from poverty, is this: what can China do to clear the air? Guests include a man who used to write China's environmental laws and a leading activist with some surprising answers. (Photo: A man and his child wear masks to protest against pollution. Credit: Getty Images)