Integrated effects of SCR, velocity, and air-fuel ration on gaseous pollutants and CO₂ emissions from China V and VI heavy-duty diesel vehicles

Vehicle exhaust, an important source of air pollution, is affected by many factors, including driving conditions, combustion efficiencies, and the usage of emission control devices. In this study, the Portable Emission Measurement System (PEMS) was used to test the emissions from China V and China VI heavy-duty diesel vehicles to evaluate the integrated effects of Selective Catalytic Reduction (SCR), velocity, and air-fuel ratio on carbon dioxide (CO₂) and nitrogen oxide (NO_x) emissions. Our results reveal that the average distance-based CO₂ and CO emission factors at high velocities (50–90 km/h) are 25% and 61% lower than those at low velocities (less than 50 km/h). The use of SCR increases CO₂ emissions in the range of 70–90 km/h (an average increase of 10.9%). In addition, SCR leads to a 55% NO_x emission reduction at low velocities and 89% at high velocities, with an overall average reduction of 84%. We also find that SCR leads to a significant reduction in the correlation between NO_x emissions and air-fuel ratio (0.76 vs 0.47 for China V truck; 0.72 vs 0.05 for China VI truck), but it does not cause a drastic reduction in the correlation coefficients between CO₂ emissions and air-fuel ratio, which can be used to detect whether SCR is working effectively.