Emission Characteristics of Nitrous Oxide (N2O) from Conventional Gasoline and Hybrid Vehicles

Considering the potential warming potential and long lifetime of nitrous oxide (N2O) as a greenhouse gas, exploring its emission characteristics is of great significance for its control and the achievement of sustainable development goals. As vehicles are a significant source of N2O emissions, in this study we conducted a detailed investigation of N2O in the exhaust of light-duty vehicles using a chassis dynamometer. We selected one conventional gasoline vehicle and two hybrid electric vehicles. We found that the N2O emissions from all the tested vehicles complied with the China 6 emission regulation, with emission factors of 7.7 mg/km, 6.8 mg/km, and 17.1 mg/km, respectively, for the three vehicles. Driving conditions played a crucial role in N2O emissions, with emissions generated primarily during extra-high-speed conditions, possibly due to the higher driving speed and greater number of acceleration/deceleration events. Furthermore, while hybrid electric vehicles emitted less NOx compared to conventional gasoline vehicles, their N2O emissions were closely tied to their engine operating conditions. Surprisingly, we discovered that hybrid electric vehicles emitted more N2O during frequent engine start–stop cycles, which could be related to the mechanisms of N2O generation. These findings contribute to a better understanding of the N2O emission characteristics of vehicles and will inform the development of emission control strategies to better promote global sustainable development.