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A sample of 21 light duty vehicles powered by Otto cycle engines were tested on a chassis dynamometer to measure the exhaust emissions of nitrous oxide (N 2 O). The tests were performed at the Vehicle Emission Laboratory of CETESB (Environmental Company of the State of Sao Paulo) using the US-FTP-75 (Federal Test Procedure) driving cycle. The sample tested included passenger cars running on three types of fuels used in Brazil: gasohol, ethanol and CNG. The measurement of N 2 O was made using two methods: Non Dispersive InfraRed (NDIR) analyzer and Fourier Transform InfraRed spectroscopy (FTIR). Measurements of regulated pollutants were also made in order to establish correlations between N 2 O and NO x . The average N 2 O emission factors obtained by the NDIR method was 78±41 mg.km −1 for vehicles running with gasohol, 73±45 mg.km −1 for ethanol vehicles and 171±69 mg.km −1 for CNG vehicles. Seventeen results using the FTIR method were also obtained. For gasohol vehicles the results showed a good agreement between the two methods, with an average emission factor of 68±41 mg.km −1 . The FTIR measurement results of N 2 O for ethanol and CNG vehicles were much lower than those obtained by the NDIR method. The emission factors were 17±10 mg.km −1 and 33±17 mg.km −1 , respectively, possibly because of the interference of water vapor (present at a higher concentration in the exhaust gases of these vehicles) on measurements by the NDIR method.

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