“…With the rapid economic development in China, there is a rapid growth in the city taxies. Until the end of 2011, there were more than 66,000 taxies in Beijing [1] , 50,000 in Shanghai, 18,000 in Guangzhou and 13,000 in Shenzhen. Because of the long mileage per year and the traffic jams in cities, the exhaust of taxies is an important source to the air pollution.…”