## 1 Introduction  
In recent years atmospheric pressure plasma jets (APPJs) produced in open environments have received a lot of attention, not only because of their versatility and ease of use, but also due to the encouraging results achieved in the most diverse applications [1; 2; 3; 4; 5]. Special attention has been given to medical and biological applications of APPJs, whose beneficial effects have been attributed to the reactive oxygen and nitrogen species (RONS) produced by the plasma jets [6; 7; 8]. The actions of the RONS are not only limited to biological materials, since they also contribute to the hydrophilization and surface activation processes of many materials treated with plasma [9; 10]. Many studies indicated that the addition of small amounts of oxygen (O\({}_{2}\)) to the gas employed to produce plasma, usually argon (Ar) or helium (He), can increase the amount of atomic oxygen (O) produced in the APPJ [11; 12; 13; 14; 15; 16; 17]. To verify this increase in the population of O most authors have measured the light emission from excited O atoms coming from the 777 nm triplet or, in some cases, from the 844 nm triplet [13]. In some works, it was found that there is an optimal O\({}_{2}\) percentage that maximizes the intensity of the O emission lines. There are also works in which the authors reported that some applications of the plasma jets, with both inorganic and biological materials as a target, showed better results when there was a small O\({}_{2}\) addition to the plasma. However, only a few works analyzed the production of other reactive species, such as OH and NO, together with the O production. In particular, [PERSON] et al [15] studied the production efficiency of RONS as a function of the O\({}_{2}\) content in the He-O\({}_{2}\) admixture, in the range from 0-2% of the total gas flow rate, and applying different voltage waveforms to generate APPJs. In that work, [PERSON] et al have found that the production efficiency of both OH and NO decreases with O\({}_{2}\) addition but the opposite occurs for the O\({}_{3}\) and NO\({}_{2}\) molecules. In the case of the production efficiency of O atoms, a peak value was observed for 0.5% of O\({}_{2}\) content. Those results were almost the same for any HV waveform applied to generate the APPJ. Regarding the effects of additional O\({}_{2}\) on APPJ parameters, the main changes reported in the literature are decrease in jet length, reduction on discharge power and current, and variations in temperatures (rotational and vibrational) [18; 19; 20; 21; 22; 23; 24]. Some works also identified an increment in the applied voltage as a function of the O\({}_{2}\) content, even with the power source configured to apply a fixed voltage to the electrodes, a fact that suggests a change in the load impedance followed by an impedance matching [25; 26]. [PERSON] et al [27] performed an investigation on the stability of APPJs as a function of the O\({}_{2}\) content in the working gas which, based on a global model for APPJs produced with He-O\({}_{2}\) admixtures, has shown that there is no discharge equilibrium if the oxygen fraction exceeds 1% in a configuration that employs a power source with frequency of 13.56 MHz and a gap of 1 mm between the electrodes. The discharge dynamics in dielectric barrier discharge (DBD) plasmas with O\({}_{2}\) in the gas admixture was studied only using N\({}_{2}\)-O\({}_{2}\) in a work aimed to investigate the transition from diffuse to filamentary regime [28]. Most studies found in the literature evaluate the production of RONS for only one fixed flow rate for the working gas, varying solely the amount of O\({}_{2}\) added to it. The present paper presents results using two different flow rates for the working gas together with the variation in the percentage of O\({}_{2}\) added to the plasma.