Air pollutants emitted by motor vehicles make a major contribution to air pollution in large urban centers, accounting for about 75% of emissions. The estimation of GHG emissions by the “Top-down” method used in the National Energy Balance - BEN, provides for the conversion of all fuel consumption measures to a common unit. Thus, the study aimed to guide the monitoring and monitoring of the concentrations of pollutant gases emitted by diesel combustion vehicles, comparing CO2 emissions in 2018, in two public and private transport fleets in the city of Manaus. - AM Based on the application of the Top-Down methodology generating the data in the comparative table of public and private transport companies, it is evident that CO2 emissions for both fleets present a high air pollution index suggesting the adaptation of the vehicle fleet. by adopting similar fuel with lower pollutant content. The data obtained in the study show that fuels with low emission factors should be used in urban public transport vehicles.