## 3 Results and Discussion
### Effects on APPJ Thermal Parameters  
The rotational and vibrational temperatures (\(T_{rot}\) and \(T_{vib}\), respectively) can be considered the main thermal parameters of APPJs, since \(T_{rot}\) has a close relationship with the gas temperature (\(T_{gas}\)) and in most cases it is being assumed that \(T_{rot}\approx T_{gas}\). In APPJs the \(T_{vib}\) is related to the rate of chemical reactions, i.e., higher \(T_{vib}\) values increase the likelihood of chemical reactions between the plasma and the target under treatment [41; 42]. Of course, the electron temperature (\(T_{e}\)) is a thermal parameter that also plays an important role in the plasma dynamics, and it is probably the one most affected by the additional \(\mathrm{O_{2}}\) injected into the plasma. However, the variations on the electron temperature could not be analyzed in this work because we do not have the appropriated tools to perform \(T_{e}\) measurements. It can be seen in Figure 7 that the \(T_{rot}\) values are not significantly affected by the additional \(\mathrm{O_{2}}\) in the plasma for all distances between the plasma outlet and the target and for the two He flow rates used, presenting variations around 550 K in almost all measurements. On the other hand, the \(T_{vib}\) curves present clear downward trends as more \(\mathrm{O_{2}}\) is added to the plasma. Additionally, the \(T_{vib}\) tends to decrease as \(\mathbf{d}\) increases. In addition, no significant variation in \(T_{vib}\) values are observed when the He flow rate was changed. Figure 6: Emission intensities of selected lines/bands from O, NO, and OH radicals as a function of the additional \(\mathrm{O_{2}}\) percentage for different \(\mathbf{d}\) values (indicated in the curve legends). The data were measured for He flow rates of 1.5 L/min in (\(\mathbf{a}\)) and 2.0 L/min in (\(\mathbf{b}\)). Symbols represent experimental data and lines are trend curves. By comparing the profiles of \(T_{rot}\) and \(T_{vib}\) values measured as a function of the additional O\({}_{2}\) in the plasma, shown in Figure 7a,b, it can be seen that at different He flow rates the behavior of the temperatures as a function of the O\({}_{2}\) content do not present significant changes. Regarding the magnitude of the temperature values, those obtained for \(T_{rot}\) are within the expected range for APPJs produced in He with the plasma jet impinging a metallic target [43]. However, those \(T_{rot}\) values are higher than the room temperature (\(\sim\)300 K) and are likely being overestimated due to the low-resolution spectrometer employed to perform the measurements. Additionally, one should consider that performing OES measurements of plasma portions that are close to the target's surface, can artificially increase the \(T_{rot}\) values. The fact that the plasma jet is directly impinging on the metallic target results in a strong plasma-material interaction, causing the release of a lot of secondary electrons to the plasma, which influences the population of higher energy rotational levels leading to higher \(T_{rot}\) values. Furthermore, since the floating wire placed inside the plastic tube is a conducting material, the plasma jet may present a corona discharge component, which can also be one of the causes of the higher \(T_{rot}\) values obtained. Concerning the \(T_{vib}\) values obtained in this work, they are much higher than those obtained for APPJs in similar conditions, being more than ten times higher than the corresponding \(T_{rot}\) values. A possible explanation for this observation is that these \(T_{vib}\) values have a close relationship with the small diameter of the plastic tube, which causes an increase in the gas pressure inside the reactor leading to an increment in \(T_{vib}\)[44]. At the same time, the plasma-material interaction may be influencing the \(T_{vib}\) values as well. In our preliminary experiments we used an infrared thermometer to monitor the target temperature during the plasma jet application.