# Evaluation of NOx Reduction Effect and Impact on Asphalt
## 3 Experimental Results and Analysis
### Evaluation of NOx Removal Performance by Reactor Type
#### 3.1.2 Mixed Tank Photo Reactor Test Result  
A mixed tank photoreactor was operated at a flow rate of 3 L/min, UV intensity of 10 W/m\({}^{2}\), temperature of 25 \(\pm\) 5 \({}^{\circ}\)C, and humidity of 45 \(\pm\) 5%. Figure 8 show the change in NOx concentration in the mixed-tank photo reactor experiment for TiO\({}_{2}\). As the reactor is larger than the bed flow photoreactor, the UV light was turned on after maintaining a stable state of NOx concentration in the reactor for approximately 100 min. Before turning on the UV light, the initial concentration in the chamber was equilibrated to 1 ppm. As with the bed flow photoreactor method, the concentrations of NOx and NO were reduced after turning on the UV light, and NO\({}_{2}\) was generated due to NO oxidation. After the experiment was performed for 5 h, the UV light was turned off, and after that, it had a slight equilibrium state for 10 min before showing a tendency to increase again. In the case of the mixed tank photoreactor method, which has a larger reactor size than the bed flow photoreactor, the reaction does not occur immediately when the UV light is turned on, and  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Test ID**} & **Total** & **Total** & **Total** \\  & **NO (umol)** & **Removed No (umol)** & **Removed No (\%)** \\ \hline Type-1 & 13.59 & 3.59 & 26.06 \\ Type-2 & 13.55 & 2.51 & 18.52 \\ Type-3 & 13.71 & 2.99 & 21.82 \\ \hline \hline \end{tabular}
\end{table}
Table 6: NO reduction and reduction efficiency of bed flow photo reactors.  
Figure 7: Variation of NOx concentrations during the bed flow photo reactor experiment.  
the NOx and NO concentrations gradually decrease until 2 h and 30 min before remaining in a parallel state. Table 7 show the NO removal efficiencies by TiO\({}_{2}\) type. In the case of Type-1, the NO removal rate was 43.66%, the Type-2 NO removal efficiency was 31.41%, and the Type-3 NO removal efficiency was 41.65%.  
In the NOx removal performance evaluation experiment of each reactor, the NOx removal rate of the three TiO\({}_{2}\) types showed a similar trend, but the NOx reduction rate of the mixed tank photoreactor method was higher. This is because the amount of TiO\({}_{2}\) used in the experiment was the same, but the NOx and TiO\({}_{2}\) contact surfaces were much larger in the mixed tank photoreactor. Only specimens of limited size can be applied to bed flow photoreceptors, whereas mixed tank photoreactors increase the contact surface with NOx because the size of the reactor is larger even if the same amount of TiO\({}_{2}\) is used. Therefore, the amount of TiO\({}_{2}\) that can react with NOx is higher than that of bed flow photoreceptors. It was found that the NOx reduction effect in the mixed tank photoreactor increased by 65%-90%. Through the mixed tank photoreactor, construction materials and secondary products that could not be tested in the existing bed flow photoreceptors (ISO standard) could be evaluated without reprocessing the specimen size, and the performance deviation from the field is expected to be reduced.