Real-world emission characteristics and driving factors of diesel trucks: Insights from plume chasing experiments

On-road transportation is gradually becoming one of the major source contributors to air pollutants and carbon emissions in China. In this study, a chasing experiment was conducted on 487 diesel trucks in Shanghai using a mobile plume chasing and analysis system to obtain the real-world emission characteristics of air pollutants and carbon dioxide (CO₂). The average emission factors (EFs) of nitrogen oxide (NOx), fine particulate matter (PM_2.5), volatile organic compounds (VOCs) and carbon monoxide (CO) of the measured vehicles are 22.8 ± 13.5, 0.38 ± 0.26, 5.6 ± 4.9, and 4.5 ± 4.0 g/kg fuel, respectively. The observed decrease in EFs of air pollutants from China IV to China VI suggests a potential correlation between stricter emission standards and reduced emissions in diesel truck fleets. Additionally, the EFs increase with the gross vehicle weights (GVW). The driving speed, registration year and wind direction were the main drivers of NOx EFs. The measured CO₂ EFs is 3182.2 ± 5.8 g/kg fuel, showing little variations with emission standards and GVW, which is different from the abovementioned air pollutants. We found a significant negative correlation between the EFs of CO₂ and NO_x (p < 0.05), indicating that as NOx emissions decrease, CO₂ emissions tend to increase. Therefore, we recommend integrating CO₂ emission limits into new standards to achieve synergistic control of pollutants and greenhouse gases.