Evaluation of real-world CO2 and NOX emissions of various in-use heavy-duty vehicles

As a major emission source in road transportation, carbon dioxide (CO2) emissions from heavy-duty vehicles (HDVs) exacerbate climate change, while nitrogen oxide (NOX) emissions pose serious health risks to human health. Therefore, it is critical to investigate in-depth their emission characteristics and evaluate the real-world emission levels of in-use HDVs, as they are an important source of mobile source emission. In this study, eleven in-use HDVs were tested using a Portable Emission Measurement System (PEMS). The results indicated that the CO2 and NOX emissions were significantly influenced by driving conditions, fuel types, load conditions, and vehicle types. The emission rates of CO2 and NOX increased with vehicle speed and acceleration. HDVs operating on urban or suburban roads exhibited the highest emission factors, with urban roads prone to generating high NO2 emissions. The China V diesel vehicle exhibited higher CO2 emission factors, while the China IV diesel vehicle demonstrated the highest NOX and NO2 emission factors. Additionally, a China V compressed natural gas (CNG) vehicle showed higher NOX emission levels compared with China V liquefied natural gas (LNG) vehicles. This study provides critical insights into the real-world emission characteristics of in-use HDVs and offers a theoretical and data foundation for formulating effective emission control strategies and regulating in-use vehicles.