# Prediction of Pollutant Emissions in Various Cases in Road Transport
## 3 Results  
The authors investigated the impact of changing the fuel type on air pollutants, where the emissions were calculated assuming the same amount and structure of fuel (mix) as was used by the number of passenger cars in 2020. Additionally, the authors investigated changes in emissions when using only one fuel type, i.e., diesel oil, gasoline, LPG, CNG, or biofuel (bioethanol and biodiesel). The comparison of annual CO\({}_{2}\), NOx, and PM2.5 emissions from passenger cars depending on fuel type is shown in Figure 3.  
The figure shows the dependence between CO\({}_{2}\), NOx, and PM2.5 emissions and fuel type. It is worth noting that for petrol (gasoline), LPG, and CNG, the generated CO\({}_{2}\) emissions were almost two times higher than those for the currently applied fuel mix and biofuel. Moreover, diesel oil produced only slightly higher emissions than the fuel mix and biofuel. According to the information above, biofuels might qualify as carbon-negative energy carriers. The emissions of NOx and PM2.5 caused by the combustion of gasoline, diesel oil, LPG, and CNG were higher than those of the currently applied fuel mix. It is worth noting that the combustion of biofuels will cause a slight increase in NOx and PM2.5 emissions compared to the presently applied fuel mix. In the cases of NOx and PM2.5, the relationship between the emissions from biofuel to the emissions from fuel mix was very similar to the case of CO\({}_{2}\). The simulation results clearly show that biofuel caused the lowest emissions of CO\({}_{2}\), NOx, and PM2.5. In the case of conventional fuels, the lowest emissions were caused by diesel-powered engines. The results of the influence of the Euro standard and the type of fuel on emissions indicated the following in the case of replacing the Polish fuel mix:  
* Gasoline would increase CO\({}_{2}\) emissions by 118%, NOx by 81%, and PM2.5 by 54%;
* Diesel oil would increase CO\({}_{2}\) emissions by 7%, NOx by 22%, and PM2.5 by 28%;
* LPG would increase CO\({}_{2}\) emissions by 154%, NOx by 94%, and PM2.5 by 77%;
* CNG would decrease CO\({}_{2}\) emissions by 1% and NOx by 2%, and increase PM2.5 by 3%;  
Figure 3: Comparison of CO\({}_{2}\), NOx, and PM2.5 emissions depending on fuel type. Biofuel emissions of CO\({}_{2}\), NOx and PM2.5 would remain at the same level. The above results show that replacing fuels from the current mix with pure gasoline, diesel oil, or LPG would increase the emission of all pollutants tested. Replacing the current fuel mix with CNG or biofuel would cause emissions to decrease slightly or stay at the same level. It is worth remembering, however, that biofuels are treated as climate-neutral fuels, so CO\({}_{2}\) emissions from their combustion are not treated as CO\({}_{2}\) emissions of anthropological origin. The comparisons of CO\({}_{2}\) emissions depending on Euro standards and fuel types are shown in Figures 4-7. Figures 4-7 show the dependence between CO\({}_{2}\) emissions and technology (Euro standard) for various vehicle types: PCs (Figure 4), LDVs (Figure 5), HDVs and buses (Figure 6), and L-category vehicles (Figure 7). For the Euro standards 1-5, in the case of PCs, LDVs, and L-category vehicles, biofuel (bioethanol) caused higher CO\({}_{2}\) emissions than petrol-fueled vehicles. For Euro standards 1-5 in the case of PCs and LDVs, and for L-category vehicles under Euro standards 1-4, the emissions from biodiesel (bioethanol) were considerably more extensive than the emissions from conventional fuels (petrol, diesel oil, LPG, and CNG). The opposite situation was observed for Euro 6 PCs and LDVs, and Euro 5 L-category vehicles. In the case of diesel oil, the combustion of biofuel resulted in lower emissions for all vehicle categories. The CO\({}_{2}\) emissions caused by the combustion of LPG and CNG in PCs were almost on the same level as those from petrol and diesel oil. It is also worth noting that for HDVs and buses, the emissions were lower for biofuel, and that emissions decreased along with the increase of the Euro standard.