# Evaluation of Turkey's Road-Based Greenhouse Gas Inventory and Future Projections
## 2 Materials and Methods
### Emission Calculations  
An approach commonly used to calculate traffic emissions involves using emission factors [13]. Emission factors are frequently employed to evaluate transport emissions by establishing a correlation between pollutant emissions and vehicle activities and types, such as distance traveled, fuel consumption, and energy consumption [32]. In this study, the number and type of vehicles and the distance traveled on state roads in Turkey, which form the basis of emission calculations, were compiled from the Traffic Transport Information Index published annually by the GDH for the 11 years between 2010 and 2020 [31]. Vehicles were classified as automobiles (Personal Cars--PCs), light commercial vehicles (LCVs), and heavy-duty vehicles (HDVs), and automobiles were classified as petrol, diesel, and LPG according to fuel type [29]. This study classified LCVs and HDVs in Turkey as diesel-fueled vehicles because they mainly use diesel fuel, with some exceptions. Emission factors from the \"EMEP/EEA air pollutant emission inventory guide 2023\" were utilized in the study. This guide is technical and supports the reporting of emission data under the UNECE Convention on Long-Range Transboundary Air Pollution (CLRTAP) and the EU National Emission Ceilings Directive. In the guide, the tiered approach for emission estimations is divided into three stages, which vary depending on the technological specifics employed in the calculation. In the Tier 1 approach, the calculation is based on the amount of each fuel type and its emission factors (Equation (1)). Compared to other methods, this method allows the collection of the data required for calculations. Tier 2 is similar to Tier 1 in that it uses activity data and emission factors to predict emissions. The primary difference is that this more detailed methodology requires additional information on fuel, technology, and country-specific details. In the Tier 3 methodology, vehicle emissions are calculated primarily based on engine operating conditions (hot-cold) and various driving situations (urban, rural, and highway driving). Factors such as cold starts, seasonal effects, and vehicle idling time can significantly affect emissions under real-world driving conditions. Newer standards (such as Tier 2 and Tier 3) consider these variables more comprehensively, but they were often overlooked under older standards such as Tier 1 [33]. If the data used in these approaches (Tier 2, Tier 3) can be provided, calculations can be more accurate overall. However, it is difficult to obtain data on these approaches for the whole country. Therefore, the calculations were performed using the Tier 1 approach. The calculations employ emission factors from Table 1, and Table 2 displays the fuel consumption data per kilometer for each vehicle category. \[\text{E}_{\text{i}}=\sum_{\text{i,m}}\left(\sum_{\text{i}}(\text{FC}_{\text{j}} \times\text{EF}_{\text{ij}}\times\text{VRL})\right) \tag{1}\]  
where \(\text{E}_{\text{i}}\) is the daily amount of emissions (g/km), \(\text{FC}_{\text{j}}\) is the fuel consumption (g-fuel/km), \(\text{EF}_{\text{ij}}\) is the emission factor (g/kg fuel), VRL is the vehicle road length (km), i is the type of pollutant, j is the fuel type, and m represents the total values for all. Data on the distribution of registered cars based on fuel type were sourced from TurkStat for 11 years. Using these rates in the calculations, the distribution of cars based on fuel type was calculated. The corresponding graph is shown in Figure 2.