# Low Temperature Plasma Strategies for
## 3 Results  
### Plasma Current Voltage and Emission Spectroscopy  
The SDBD was operated in humid ambient air (25 \({}^{\circ}\)C, 40% RH) at atmospheric pressure. The applied AC voltage (20.6 kVpp (peak-to-peak); see Figure 2) consisted of repetitive bursts (repetition rate 500 Hz), each consisting of nine AC cycles (fAC = 19.6 kHz) with a repetition rate of 500 Hz (duty cycle of 0.25). In this way, we obtained a homogeneous distribution of micro-discharges. The actual discharge ON-time is shorter than the duration of the AC cycles. We can estimate an effective duty cycle of the order of 0.1 of the nominal one. This ensures that biological samples are not exposed to excessively damaging temperatures. Typical voltage, current, and charge characteristics are shown in Figure 2A-C, along  
Figure 2: Typical waveform for 1 burst applied to the discharge reactor: (**A**) voltage; (**B**) current; (**C**) charge; (**D**) Lissajous figure for estimating the burst energy deposited in the plasma phase. with the typical Lissajous figure showing the charge voltage characteristic (Figure 2D) used to determine the discharge energy. The estimated energy per burst is about 4.5 mJ, i.e., an average power of 2.25 W, with an energy density of 3.8 10\({}^{-2}\) Wh L\({}^{-1}\). With this energy density, the air-SDBD is operated in ozone mode, and we can expect a concentration on the order of 200-300 ppm, well above the concentration of nitrogen oxide products [30]. The total power consumption of the plasma device was measured and estimated at 5W with an energy transfer to the plasma of 45%. Figure 3 shows low-resolution emission spectra of filamentary SDBD operating in humid air and reveals strong bands of the second positive system (SPS) (C\({}^{3}\Pi_{\mathrm{u}}\to\) B\({}^{3}\Pi_{\mathrm{g}}\)) of N\({}_{2}\) and the first negative system (FNS) (B\({}^{2}\Sigma_{\mathrm{u}}{}^{+}\to\) X\({}^{2}\Sigma_{\mathrm{g}}{}^{+}\)) of N\({}_{2}\) in the UV spectral region. In the Vis-NIR region, we observed characteristic sequences of bands of the first positive system (FPS) (B\({}^{3}\Pi_{\mathrm{g}}\to\) A\({}^{3}\Sigma_{\mathrm{u}}{}^{+}\)) of N\({}_{2}\). The emission line for atomic oxygen was observed at 777 nm, indicating the production of atomic oxygen during the plasma phase. A detailed analysis of the emission spectra allows the measurement of the gas temperature and the local reduced electric field, E/N, i.e., the electric field divided by the concentration of gas molecules. Moreover, a reasonable estimation of the nitrogen vibrational temperature (T\({}_{\mathrm{v}}\)) is possible. There is no room here to explain the complex analysis procedure that can be found in [80; 81]. It is important here to point out that this analysis is based on the fact that the observed emissions originated from electronic states that are populated by electron impact. In other words, these emissions come from the active discharge sites, i.e., the micro-discharges, and therefore, the quantities inferred are \"average\" values within the micro-discharges. In this way, they are representative of the conditions that initiate the plasma chemistry by excitation and dissociations induced by electron impact. The gas temperature, in such conditions, is equal to the rotational temperature of the emitting molecules. The partially resolved structures of SPS (0,0) shown in Figure 4 were analysed using the Massive OES spectroscopy tool [74; 75; 76]. The SPS (0,0) band can be fitted for a specific instrumental function by setting the rotational temperature to 350 \(\pm\) 25 K.  
Figure 3: Typical averaged (1000 shots) electron impact induced emission spectrum intensity (I(a.u.)) as a function of wavelength (\(\lambda\)(nm)) over multiple discharge filaments developing over the entire ON time AC HV burst. This temperature represents the gas temperature, during the discharge on phase, of the plasma that is confined just a few hundred micrometres above the dielectric surface.