Metrological greenhouse gas emission assessment of the transport sector in Türkiye: Towards instrumentation, uncertainty and trends

Environmental issues, including global warming, dependence on fossil fuels, deforestation, and rising CO2 emissions, have become major challenges worldwide. In Türkiye, fossil fuel demand has continued to rise over the past two decades, despite policies promoting renewable energy. The effectiveness of these policies on transport-related greenhouse gas (GHG) emissions remains uncertain. To address this gap, this study analyses the long-term evolution of transport emissions over the last 33 years, integrating inventory-based estimates with experimental measurements to provide a metrologically validated dataset. Portable exhaust gas analysers (Horiba PG-350 and Testo 350XL) were used in conjunction with calibrated thermal mass flow meters and thermocouples to quantify CO2, CH4, and N2O emissions across various vehicle types and load conditions. Calibration traceability and uncertainty estimation were performed in accordance with ISO/IEC 17025 and the GUM guidelines. Experimental results were compared with IPCC Tier 2 estimates, showing close agreement for CO2 (± 3.8 %) and larger variability for CH4 and N2O. These findings highlight the essential role of metrology in improving the reliability of emission data and support the integration of measurement-based validation into national GHG inventory frameworks.