Measurement report: Real-world assessment of the effects of emission control technology upgrades on greenhouse gas emissions from heavy-duty diesel trucks

The increasing greenhouse gas (GHG) emissions from China's transportation sector, especially those from heavy-duty diesel trucks (HDDTs) which remain insufficiently addressed. The tightening of emission standards and the widespread adoption of advanced after-treatment systems have altered the GHG emission profiles of HDDTs significantly, raising concerns about potential trade-offs between regulated pollutants and unregulated GHG emissions. This study comprehensively investigates the real-world emission characteristics of key GHGs (CO2, N2O, and CH4) from HDDTs spanning China IV to China VI standards, and quantitatively evaluates the specific role of after-treatment configurations. The results revealed a critical trade-off: although China VI vehicles achieved significant reductions in CH4 emissions (75–92% lower than China IV/V vehicles), they exhibited dramatically elevated N2O emissions,approximately 15 and 65 times higher than those of China V and IV vehicles, respectively. Consequently, N2O contributed 7.43% to the total CO2-equivalent emissions of China VI HDDTs, becoming a non-negligible component. The controlled experiment revealed that the ammonia slip catalyst (ASC) was the decisive factor, causing a 72-fold increase in the N2O concentration compared with that in the other configurations. This study provides evidence that modern after-treatment technologies, particularly the ASC mandated for China VI compliance, have inadvertently caused N2O to contribute significantly to the carbon footprint of diesel trucks. These findings underscore the necessity for future emission regulations and technology pathways to adopt an integrated, multipollutant perspective that addresses nitrogen oxides, ammonia slip, and secondary nitrous oxide formation simultaneously to truly decarbonize the heavy-duty transport sector.