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 CO2, N2O, and CH4 emissions from 12 in-use LDDTs in China. Results reveal that China's CH4 emission rates from LDDTs are overestimated by 57.71 ± 39.15 % if using the previous ratio method of CO2:CH4. 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 N2O production, which is highly sensitive to system temperature. Moreover, uphill roads can increase CO2 emissions by 51.93 % compared to downhill roads. Despite the tightening of vehicle emission standards, CO2 and N2O emissions from the LDDTs have not decreased linearly. However, LDDTs meeting the China VI standard exhibit the lowest average CO2, N2O and CH4 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.