LAUSR

Abstract Emission factors (EFs) are empirical functions that envisage the amount of an emitted pollutant based on travel activity and vehicle characteristics. This paper aims to estimate on-road gaseous emission factors of gasoline passenger vehicles under urban Malaysian road traffic conditions. Eleven vehicles were tested and the carbon monoxide (CO), carbon dioxide (CO2) and nitrogen oxides (NOx) emission results were analyzed according to driving conditions. The effects of inter-vehicle variability in terms of accumulated mileage on emission factors were explored using regression analysis. The links of real driving condition on exhaust emissions were examined using hierarchical cluster analysis. The emission factors of CO, CO2 and NOx were calculated using a fuel-based approach. The 95% confidence intervals obtained for the population mean of emission factors were CO: 0.76 ± 0.15 g/km, CO2: 236.02 ± 14.98 g/km, NOx: 0.23 ± 0.03 g/km. Vehicle age as echoed by accumulated mileage was responsible for the increase in the average emission factors of CO and NOx. The results of the cluster analysis formed four meaningful clusters which described driving conditions and exhaust emissions. Higher observations were recorded for Cluster 1 (43.25%) indicating low vehicle speed and better fuel efficiency produced low NOx and CO emissions but high CO2 emissions. The measurements reported in this paper highlight the significance of this work in quantifying CO, CO2 and NOx emissions from gasoline passenger vehicles under real-world driving conditions of urban street in Malaysia where there is a paucity of EFs studies.