The Effect of Ambient Temperature on the Emissions of Some Nitrogen Compounds:A Comparative Study on Low-, Medium- and High-Mileage Three-Way Catalyst Vehicles

Using fast FTIR-technology (Fourier Transform Infra-Red) to complement the normal regulated emission analysis, VTT Energy has performed exhaust emission measurements for several light-duty motor vehicles (passenger cars) representing a variety of current level technologies, mostly employing a three-way catalytic converter. Tests have been performed using standardized test procedures and driving cycles (U.S.EPA and ECE/EEC). Apart from the basic technology of the vehicle, ambient temperature has also been varied. Most of the tests are run at +20 to +22 °C ambient temperature, but additional tests have been carried out at ±0°C, -7 °C and even at -20 °C.

Test results suggest that nitrous oxide output varies largely from vehicle to vehicle, and its is also dependent on the ambient temperature. Most significant factor, however, seems to be vehicle mileage, or rather catalyst activity, as already suggested in previous studies. Furthermore, the detailed time resolved analysis supports the theory presented in the literature, that nitrous oxide is formed in a three-way catalytic converter within certain temperature range below the normal operating temperature.