Abstract: Taxi emissions are an important source of urban air pollution,so controlling emissions from high emission taxis is critically important for air quality improvement.Six representative high mileage gasoline taxis in Beijing were chosen,and the effects of vehicle maintenance and replacement of the three-way catalytic converters(TWCs) on fuel consumption and emissions were comprehensively assessed.In addition,the deterioration of the TWCs after replacement was also evaluated.The results indicated that common maintenance could significantly improve the fuel efficiency by about 2%-4%,but it had little effect on THC and NOx emissions.When the TWCs were replaced,greater emission reductions occurred for the taxis with higher original emissions.Furthermore,the difference between emission reduction by only replacing the first TWC versus replacing both the first and second TWC was negligible.The average reductions of CO,THC and NOx emissions from the four taxis were 45%,26% and 29%,respectively,even after traveling 185,000 km with the replaced TWCs.This indicated that the replaced TWCs could remain effective for the reduction of gaseous pollutant emissions within 200,000 km.