Mumbai, Sept. 16 -- In an encouraging sign in the fight against air pollution in the city, a study indicated that biofuel emissions - one of the top sources of particulate matter - are on a steady decline. The study on fuel-usage pattern has shown that 19 out of every 20 slum settlements in Mumbai prefer liquefied petroleum gas (LPG) for cooking, over other fuels such as kerosene, coal or wood....