Real-world greenhouse gas emission characteristics from in-use light-duty diesel trucks in China.

The transportation sector is a significant contributor to greenhouse gas (GHG) emissions in China. However, real-world GHG emissions from in-use light-duty diesel trucks (LDDTs) are largely uncertain due to data paucity. In this study, we have conducted real driving emission (RDE) tests of real-world CO, NO, and CH emissions from 12 in-use LDDTs in China. Results reveal that China's CH emission rates from LDDTs are overestimated by 57.71 ± 39.15 % if using the previous ratio method of CO:CH. Notably, under real-world driving conditions, such as speeds exceeding 60 km/h, maximum exhaust gas temperatures are reached, potentially impacting urea decomposition catalyst temperatures and subsequently influencing NO production, which is highly sensitive to system temperature. Moreover, uphill roads can increase CO emissions by 51.93 % compared to downhill roads. Despite the tightening of vehicle emission standards, CO and NO emissions from the LDDTs have not decreased linearly. However, LDDTs meeting the China VI standard exhibit the lowest average CO, NO and CH emission factors (EFs) of 335.26 ± 21.72 g/km, 2.7 ± 0.69 mg/km and 3.50 ± 0.70 mg/km, respectively. At last, the uncertainties in the GHG EFs for the tested LDDTs through RDE tests were (-39 %, 82 %) in our study, while a significantly higher uncertainty (-85 %, 182 %) for GHG EFs of LDDTs were found in our study and other reported literature in China, largely due to the application of different non-native vehicle emission factor models and testing methods, as well as different vehicles of control emission standards. Our study highlights more urgent needs for direct RDE tests and the importance of considering real driving conditions, such as road grades, in special geographical regions when undertaking carbon accounting work in the transportation sector.