Speed-dependent representative emission factors for catalyst passenger cars and influencing parameters

This paper presents speed-dependent hot emission factors for passenger cars equipped with a three-way catalyst. The emission factors were developed using emission data from in-use vehicles based on chassis dynamometer tests conducted over real-world driving cycles. The variability of the emission data and the use of cycles with different characteristics resulted in a low correlation between emission factors and mean travelling speed. Analysis of the data identified differences in vehicle emission performance as the main source of variability. The potential for decreasing emission variability by classifying vehicles according to their engine capacity and mileage was studied by means of an analysis of variance test. Results showed that CO, NOx and HC emissions were dependent on mileage but not on engine size. Emissions of CO2 were found to be strongly dependent on engine size, but insensitive to vehicle mileage.