According to the scheme, the GPCB will first define the total mass of pollution that can be released into the air over a certain fixed period by all industrial units together. This will be equivalent to the cap. The permits would then become units which could be bought and sold under the ETS. "This is like the commodities you trade on the national commodity exchange," a senior GPCB official said.

The pollution board picked Surat since it is a densely-populated industrial centre and the textiles and dyeing houses there produce heavy air pollution, officials said.