Measurement report: Insight into Greenhouse Gas Emission Characteristics of Light-Duty Vehicles in China Driven by Technological Innovation

Abstract. Greenhouse gas (GHG) emissions represent a pivotal driver of global climate change, with vehicular emissions, particularly from light-duty vehicles, emerging as a prominent source of GHGs. Despite extensive research on gaseous pollutants, studies on GHG emissions within the framework of carbon neutrality remain scarce. This study delves into the emission characteristics of three primary GHGs (carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O)) from various light-duty vehicles, encompassing conventional gasoline and hybrid vehicles, and bi-fuel taxis. As anticipated, with advancements in emission standards and powertrains, vehicular GHG emissions have significantly decreased. However, our findings also revealed surprising trends. While engine technology upgrades reduced CO₂, they unexpectedly increased CH₄ and N₂O emissions. Additionally, hot starts, beneficial for reducing CO₂ and CH₄ emissions, caused heightened N₂O emissions, which is noteworthy under operating conditions with frequent start-stop events. Intriguingly, compressed natural gas (CNG), generally perceived as cleaner, increased CH₄ emissions. Regarding the impact of Three-Way Catalysts (TWC) on GHG emissions, under “TWC failed” conditions, N₂O emissions from CNG-powered vehicles were approximately three times higher than those under “TWC worked” conditions, attributed to the significant increase in NOx. Considering the global warming potential (GWP), the "TWC failure" scenario paradoxically decreased GWP values, highlighting the complex interaction between emission control technologies and their environmental impacts. This study provides crucial insights into vehicular GHG emissions, which are essential for developing effective strategies aimed at mitigating emissions and enhancing the efficiency of emission control systems.