Abstract: Objective　Human activities have intensified the emission of greenhouse gas CO2, which is one of the important factors contributing to the exacerbation of global warming. To address this challenge, China has proposed a dual carbon strategy goal. In this context, promoting the development of new energy vehicles has become a pivotal strategy for controlling atmospheric pollution and mitigating climate change. Hybrid electric vehicles (HEVs), due to their notable energy-saving advantages, represent an effective pathway for the transformation of automotive industry. As a result, the actual emission characteristics of HEVs have attracted great attention in current research on motor vehicles. Unlike traditional gasoline vehicles, HEVs exhibit distinct emission characteristics due to differences in drive system configurations and energy management strategies. However, regulatory laboratory conditions and real driving emissions (RDE) test protocols have inherent limitations in capturing the full spectrum of vehicle emissions in actual urban driving scenarios. To address this issue, this study employs Global Positioning System (GPS) devices to collect real-world vehicle trajectory data from urban road networks, with a focus on representative urban driving conditions and their micro-condition unit distributions. And then, RDE tests are conducted to measure the real-world emission rates of HEVs operating in charge-sustaining (CS) mode, and their transient emission characteristics are analyzed in detail. Methods　Firstly, real-world vehicle trajectory data are collected through GPS. Then, using the method of "short travel division-characteristic parameters calculation-principal component analysis-cluster analysis-correlation coefficient", typical driving cycles are constructed. At the same time, the portable emission measurement system (PEMS) is used to conduct real road emission tests and obtain transient emission rates of HEVs. Finally, by calculating the vehicle specific power (VSP) of HEVs and dividing them into micro operating units, and combing the average emission rate of each unit obtained from testing with the unit time distribution of the real driving cycle constructed, the comprehensive emission factors of the HEVs under real road conditions are calculated. Results and Discussion　The total duration of the typical real-world driving cycle constructed in the study is 1800 seconds, with an average speed of 30.24 km/h. Its micro-operation modes show that the proportion of low-speed and idling conditions is prominent, with idling accounting for nearly 25%, indicating frequent traffic congestion on actual roads. The emission test results show that in CS mode, the peak emission rates of carbon monoxide (CO) and particulate number (PN) occur in the low-speed range of 20–50 km/h, while the peak emissions of nitrogen oxides (NOx) are concentrated in the high-speed range of 90–110 km/h. Within the same speed range, the emission rates of the three pollutants all increase with the increase of VSP. By coupling the micro-time distribution of real-world driving cycle with the measured emission rates, the emission factors of CO, NOx, and PN are calculated as 194.38 mg/km, 10.89 mg/km, and 4.13 × 1010 #/km, respectively. Compared with traditional gasoline vehicles of the same emission standard, hybrid electric vehicles do not show significant emission reduction advantages in terms of CO and PN emissions in CS mode. This may be due to the frequent start-stops of engine during driving, resulting in incomplete combustion and reduced working efficiency of the three-way catalytic converter (TWC). Conclusions　To investigate the emission characteristics of HEVs under actual road conditions, we construct a typical driving cycle based on real driving data and couple it with RDE tests data to obtain the real emission factors. The results show that the constructed driving cycle reflects congested urban conditions, characterized by a high proportion of low-speed and idling segments, which may increase pollutant emissions. In CS mode, the peak emissions of CO and PN are concentrated in the low-speed range, while those of NOx occur in the high-speed range, and the emission rates of all pollutants increase with the increase of power demand. Compared with the results of other studies, the real emission factors of CO, NOx, and PN obtained through fitting in this work are within a reasonable range. Compared with conventional gasoline vehicles of the same standard, HEVs in CS mode do not show significant advantages in reducing CO and PN emissions, and the frequent start-stop of engine may affect the combustion efficiency and the performance of after-treatment devices. The research results indicate that a more comprehensive evaluation of the emission performance of HEVs under different operating modes is needed.

Key words: hybrid electric vehicles, driving cycle construction, emission characteristics, micro operating condition