## 2 Materials and Methods
### Calculation Model  
At first, the emission factors per km traveled (VKT approach) per type of vehicle and per type of pollutant were calculated (Table 1). The COBERT methodology, a European tool developed in Microsoft Windows, was used [13]. This tool calculates the emissions by road vehicles per pollutant. COBERT v.5 was used to calculate the emission factors of cars, buses, motorbikes, and trucks. For Underground and Tram, emission factors were extracted from \"The circular lab\" [17], \"Ferrocarrils de La Generalitat de Catalunya\" [18], \"Observatorio de Costes del Transporte de Mercancias por ferrocarril\" [19] and \"Observatorio de transporte y logistica de Espana\" [20]. The factors were calculated using the rule of three by inference from the data obtained from the repositories consulted.  
Then, as the matrix gives the total number of trips, the statistics of the service of transport used for each combination were calculated. We use \"statistics\" to refer to the proportion of the total trips made by each type of vehicle, that is, the percentage of total trips made by cars, buses, etc. With the help of the survey database, the number of journeys made by each of the vehicle types studied was calculated. In addition, each statistic was calculated according to the distance traveled for each trip. The final table with the calculated statistics is shown in Table 2.  
As can be seen, the remaining percentage is modes of transport that do not emit pollutants, such as walking or cycling.  
On the other hand, the routes of the journeys produced by mobility were geolocated. For this, it was necessary to have the journeys' origin and destination points. As the mobility information came from 560 transport zones, these trips have a mobility zone as their origin and destination. Therefore, the centroid of each mobility zone was calculated and forced to fall within it.  
The point of origin and the point of destination of each displacement were selected. These were entered into each transport network to obtain what the journey would be like depending on the means of transport used. The number of journeys of that combination with that service of transport was calculated based on the number of journeys in the matrix,  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**g/km** & **Car** & **Bus** & **Underground** & **Train** & **Motorcycle** & **Truck** \\ \hline CO\({}_{2}\) & 170.6167 & 48.5397 & 25.9500 & 31.6872 & 110.4280 & 283.5384 \\ NOX & 0.4003 & 0.3323 & 0.0280 & 0.0055 & 0.1847 & 0.9554 \\ PM10 & 0.0136 & 0.0068 & 0.0190 & 0.0002 & 0.0559 & 0.0425 \\ \hline \end{tabular}
\end{table}
Table 1: Emission factors of each mode of transport per km traveled.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Interval** & **Car** & **Bus** & **Underground** & **Train** & **Motorcycle** & **Truck** & **Total** \\ \hline \textless{}3 km & 0.2299 & 0.0635 & 0.0113 & 0.0006 & 0.0106 & 0.0018 & 0.3177 \\ 3–5 km & 0.4177 & 0.1964 & 0.0526 & 0.0006 & 0.0237 & 0.0033 & 0.6943 \\ 5–10 km & 0.5693 & 0.1551 & 0.1115 & 0.0042 & 0.0254 & 0.0045 & 0.8700 \\ 10–20 km & 0.7564 & 0.0553 & 0.1044 & 0.0111 & 0.0174 & 0.0042 & 0.9488 \\ \textgreater{}20 km & 0.8386 & 0.0608 & 0.0380 & 0.0190 & 0.0099 & 0.0046 & 0.9709 \\ \hline \end{tabular}
\end{table}
Table 2: Statistics for each mode of transport by distance interval.  
which, multiplied by the corresponding statistic according to the distance of the journey and the type of vehicle (Table 2), gives the total number of times that journey with that service is made in a day. This process was repeated with each of the combinations of journeys proposed by the matrix. This point of the process is the 4.2 in the Figure 2, where we can see all the methodology in the Figure 2.