As a result of its rapid economic development and large volume of coal burning, China is faced with serious coal-smoke pollution in urban areas. In large cities such as Beijing and Chongqing, people are clearly suffering the adverse health effects of coal-smoke pollution, with PM-10 and SO2 as the main pollutants. Natural gas, although not the dominant energy source in China, is becoming one of the most attractive clean substitutes for coal. On one hand, there is widespread disagreement and doubt about the rationale for burning natural gas instead of using it as a  raw material in the chemical industry. On the other hand, the economic advantages of natural gas over clean-coal technology are crucial in deciding whether to promote the use of natural gas as a fuel. This research has four goals