If the citizens of Mexico City -known to be one of the most polluted cities in the world -want to breathe cleaner air, they must first take care of their kitchens. For, Sherwood Rowland, an atmospheric chemist working with the University of California has come up with a startling report which claims that liquified petroleum gas (LPG), or cooking gas, used by the 15 million people liv- ing in Mexico City is as much to be blamed for the pollution as the cars and the factories.

LPG spews into the atmosphere propane, isobu- tane and butane. Since Mexico lies in an earth - quake-prone zone, there are no gas pipelines; the con- sumers buy gas in canisters, which are refilled once a month. And around 2 mil- Ion canisters are in use in Mexico at any point of time; which means that 30,000 to 50,000 canisters are being changed everyday. "There are lots of possibilites for leakage," says Rowland. The canisters can leak in the fac- tory, leak when they are being refilled and even leak when they are being used at home.