## 4 Conclusions  
In this work we have demonstrated that the addition of O\({}_{2}\) to the working gas for generation of APPJs affects most of the plasma parameters, the production of RONS and the discharge duration and its time of ignition. Regarding the electrical parameters, the discharge power starts to decrease significantly if more than 2% of O\({}_{2}\) is added to the gas admixture while the effective current is always reduced when any amount of O\({}_{2}\) is added.  
Figure 7: Variation of \(T_{rot}\) and \(T_{vib}\) values as a function of the additional O\({}_{2}\) percentage for different **d** values. The temperatures were measured for He flow rates of 1.5 L/min in (**a**) and 2.0 L/min in (**b**). Symbols represent experimental data and lines are trend curves.  
Concerning the plasma thermal parameters, we have seen that the \(T_{rot}\) values remains almost unchanged towards the addition of O\({}_{2}\), while the \(T_{vib}\) ones presented downward tendency when small amounts of O\({}_{2}\) are added (less than 1%) followed by stable \(T_{vib}\) values for higher O\({}_{2}\) percentages. An interesting observation is that the trends exhibited by those parameters did not change if the operating conditions (mainly distance between the plasma outlet and the target and the He flow rate) are modified. On the other hand, the production of RONS presented different behaviors in their variations depending on the specie under study and on the operating conditions. As an example, the trend in the production of NO as a function of the O\({}_{2}\) content seems to be affected by both He flow rate and distance between the plasma outlet and the target.  
The aim of most works reported in the literature as well as the current one, has been to enhance the production of RONS in the plasma by addition of O\({}_{2}\) to the working gas. However, using the configuration presented in this work it was verified that the O\({}_{2}\) fulfills this goal only considering the production of atomic oxygen, which showed significant increases in almost all studied conditions when \(\sim\)0.5-0.6% of O\({}_{2}\) is added to the gas admixture. One can speculate that the production of other RONS, such as O\({}_{3}\) or NO\({}_{2}\), is probably increasing with the increment of O atoms in the plasma jet, although we have not carried out the measurements that would prove that.  
Then, as a general conclusion, we can say that the addition of O\({}_{2}\) to the working gas used to generate APPJs certainly provides an increase in the amount of O atoms in the plasma jet. However, using the configuration described in this work, the simple act of adding O\({}_{2}\) to the plasma does not necessarily imply in an increment of other RONS species, such as OH and NO, which also play important roles when the interaction between plasma and materials occurs. However, we have found that there are also ways to improve the amount of RONS other than O atoms when O\({}_{2}\) is added to the plasma by setting appropriately and carefully select some operation parameters such as the distance between the plasma outlet and the target. Nevertheless, it is important to take into account what kind of reactive specie is required by the application in question and the target under treatment to choose the best setup for the occasion.  
The authors declare no conflict of interest.