Air pollution in India is caused by fumes from cooking on wood or dung indoors in villages, and a combination of traffic exhaust, soot and construction dust and factory emissions in the cities.

Now Gujarat has launched the world’s first “cap and trading” programme to curb particulate air pollution.

Put simply, the government sets a cap on emissions and allows factories to buy and sell permits to stay below the cap.

It is being launched in the dense, industrial city of Surat, where textile and dye factories are a major source of pollution. Since 2011, local pollution control authorities have been working on the impact of emissions trading in Surat, along with the University of Chicago and Harvard University.