Non-CO2 Greenhouse Gas Emissions from Road Transportation in Türkiye: A Well-to-Wheels Assessment of Methane and Nitrous Oxide

Mitigating climate change requires greater attention to non-carbon dioxide (non-CO2) greenhouse gas (GHG) emissions from the transportation sector, particularly methane (CH4) and nitrous oxide (N2O), which remain considerably less investigated than CO2. This study presents a Well-to-Wheels (WTW) assessment of CH4 and N2O emissions from road transportation in Türkiye using the Greenhouse Gases, Regulated Emissions, and Energy Use in Technologies (GREET) model. Historical vehicle fleet data covering the period 2013–2023 were used to characterize WTW emission intensities, while hypothetical scenarios for 2040 and 2050 were evaluated under alternative electricity generation pathways representing distinct energy-generation conditions. The analysis encompasses passenger cars, sport utility vehicles, and heavy-duty vehicles with internal combustion, hybrid, plug-in hybrid, battery electric, and hydrogen fuel-cell powertrains. The results demonstrate that WTW CH4 and N2O emission intensities vary among vehicle technologies and energy pathways over the study period. The lowest emission intensities are generally obtained for battery electric and fuel-cell vehicles under electricity-generation pathways based on renewable and nuclear energy sources. The findings further indicate that hybrid technologies can provide measurable short- to medium-term mitigation benefits, although their WTW CH4 and N2O emission intensities remain dependent on the corresponding vehicle and energy pathways. This study provides a Türkiye-specific Well-to-Wheels assessment of CH4 and N2O emission intensities from road transport across the historical period and hypothetical future electricity-generation scenarios, providing a basis for evaluating non-CO2 greenhouse gas emissions associated with alternative transportation technologies and energy pathways.