Establishment of emission standards is an important measure for controlling vehicle exhaust. This study examined the emission factors of air pollutants from 40 four-stroke motorcycles of various emission standard phases, ages, and mileage. Based on the emission standards, the motorcycles were divided into three groups (Phases III, IV and V). Regulated air pollutants (CO, HC, and NOx), CO2, and 52 volatile organic compounds were evaluated on a chassis dynamometer using the Economic Commission for Europe (ECE) test cycle. The sequence of CO and HC emission factors was Phase III > Phase IV > Phase V, and their ratios of emission factor of Phase IV to Phase III and Phase V to Phase III were 0.66 and 0.42 for CO and 0.61 and 0.57 for HC, respectively. Exhaust from motorcycles deteriorates with age and mileage. For NOx emission, the sequence of emission factor was Phase V > Phase IV > Phase III. However, the relationship was insignificant between CO2 emission factor and motorcycle age. The total VOC emissions of Phase V motorcycles were the lowest (0.59 g km–1) among all test motorcycles; however, the fraction of VOC groups was similar among all test motorcycles regardless of different regulation phases. For organic air toxics, the emissions of benzene, toluene, ethylbenzene, and xylene (BTEX) decreased by 37–58% and 44–62%, respectively, for Phases IV and V motorcycles compared to those of Phase III motorcycles. Results also indicated that the ozone formation potential (OFP) was high in older motorcycles with high mileage. In summary, emissions of CO, HC, total VOCs, BTEX, and OFP may decrease with the decrease of motorcycle age and mileage as well as the phase of emission standards. The results implied that tightening emission standards indeed encourages motorcycle manufacturers to improve engine technology and combustion efficiency, resulting in reduced emission of air pollutants, except NOx emission in this study.
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