## 3 Results
### Plasma Optical Emission Spectroscopy  
The emission spectra of excited atoms and molecules in the SDBD plasma were first measured using the OceanOptics Maya 2000 spectrometer, which covers a broad spectral range from 200 nm to 1100 nm. Figure 4A,B shows typical emission spectra (averaged over  
Figure 3: Travel distance of the plasma front during pseudo-Trichel and streamer discharge modes for both types of reactors. 60 s) recorded for reactors with planar and cylindrical electrodes, respectively. Emission peaks and bands were identified and are summarized in Table 1.  
Both spectra look similar; however, the emission intensity of the plasma generated using the planar electrode is approximately twice that of the cylindrical electrode. This difference was expected, since the wire electrode suppresses the formation of streamers, as shown in Section 3.1. Both spectra are dominated by the characteristic optical bands of the N\({}_{2}\) molecules. We identified the N\({}_{2}\) s positive band (C\({}^{3}\Pi\)\(\rightarrow\) B\({}^{3}\Pi\)) in the 300 nm-500 nm range and the N\({}_{2}\) first positive band (B\({}^{3}\Pi\)\(\rightarrow\) A\({}^{3}\Sigma\)) in the 630 nm-900 nm range, along with the N\({}_{2}\)\({}^{+}\) first negative band (B\({}^{3}\Sigma\)\(\rightarrow\) X\({}^{2}\Sigma\)) at 393.1 nm. The emission spectra also contain atomic nitrogen and oxygen lines at 818.6 nm and 844.8 nm, respectively. However, for the reactor with the planar electrode, we observed a significant reduction in the intensity of the atomic nitrogen line. In particular, the expected OH bands around 308 nm were not detected [46; 47; 48]. This is probably due to overlap with much stronger N\({}_{2}\) bands, making it difficult to clearly resolve these lines. The presence of NO bands in the 200-300 nm spectral range was also expected [49]. However, the low peak intensities observed in this range prevented clear identification of these bands. Figure 4: Emission spectra of the SDBD plasma reactors with (**A**) planar electrode, (**B**) cylindrical electrode. As shown elsewhere [50; 51], the DBD plasma does not reach local thermodynamic equilibrium, so a simple Boltzmann plot method [52; 53] cannot be directly applied to determine its thermodynamic parameters. Instead, we used the Specair software (version 3.0.2.0) to simulate the N\({}_{2}\) emission spectrum at given rotational (T\({}_{\rm rot}\)), translational (T\({}_{\rm Trans}\)), vibrational (T\({}_{\rm vib}\)), and electron (T\({}_{\rm e}\)) temperatures, and fit the simulated spectrum to the measured one. However, we found that the spectral resolution of the Maya 2000 spectrograms was too low for reliable spectral fitting, so we re-measured the plasma emission spectrum using an Andor Mechelle 500 high-resolution spectrometer. Because of its relatively low sensitivity and nonlinear response over a wide spectral range, we limited its spectral range to approximately 365-384 nm, where only strong N\({}_{2}\) bands are present. This limited range also minimized simulation errors due to software limitations, such as the lack of consideration of plasma optical thickness and air absorption. In the simulations, we assumed that the plasma contained only nitrogen and that only the second positive nitrogen transitions occurred in the plasma. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Band or Line Number** & **Wavelength [nm]** & **Band** \\ \hline
1 & 296.2 & N\({}_{2}\) SP \\
2 & 312.2 & N\({}_{2}\) SP \\
3 & 314.1 & N\({}_{2}\) SP \\
4 & 316.9 & N\({}_{2}\) SP \\
5 & 336.6 & N\({}_{2}  
Figure 5 shows the measured emission spectrum for the planar electrode reactor and the fitted simulated spectrum. The multivariable iterative fitting method was used with the plasma temperatures (T\({}_{\text{Rot}}\), T\({}_{\text{Trans}}\), T\({}_{\text{Vibr}}\), T\({}_{\text{e}}\)) as the fitting parameters. The parameters that gave the best fit represent the determined values of the plasma temperatures.