## 3 Results and Discussion
### Axial Temperature Distribution  
Since this paper deals with non-thermal plasma (cold plasma), the temperature of the emerging jet from the APPJ is a critical factor in inactivation processes [30,31]. Figure 8 shows the axial distribution of temperature from the nozzle of the APPJ to a far away axial distance, at different powers of argon discharge using 1 slm of argon flow rate. The temperature depends on the input power, which ranges from 1 to 2.5 W. The temperature recognizably decreases far away--321 and 332 K at the nozzle (0 mm) to values from 310 to 319 K at 22 mm from the nozzle. The variation in the axial temperature distribution for argon discharge at different applied flow rates is shown in Figure 9. As the flow rate increases from 0.2 to 4 slm, the axial temperature decreases from 487 to 364 K at the nozzle, and from 396 to 364 K at 14 mm from the nozzle.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Axial Length** & \multicolumn{1}{c}{**Oxygen**} & \multicolumn{1}{c}{**Oxygen**} & \multicolumn{1}{c}{**Oxygen**} & \multicolumn{1}{c}{**Oxygen**} \\ \cline{3-5} **of the Jet (mm)** & **Ratio 0.25\%** & **Ratio 0.50\%** & **Ratio 1\%** & **Ratio 1.5\%** \\ \hline
13.2 & \multirow{2}{*}{**Width (mm)**} & 0.455 & 0.51 & 0.455 & 0.4 \\ \cline{1-1} \cline{3-5}
15.4 & & 0.561 & 0.561 & 0.707 & 0.854 \\ \hline
17.6 & & 0.561 & 0.756 & 0.853 & 1.196 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Largest width of the jet for oxygen/argon admixture discharge and the equivalent length.  
Figure 8: Axial distribution of temperatures from the nozzle of the plasma source at different powers for argon discharge.  
Figure 9: Axial temperature distributions for argon at different applied flow rates.  
Figure 10 shows the relation between the oxygen ratio (with 1 slm of argon flow rate) and the axial temperature of the emerging jet at different axial locations. When the flow rate of oxygen increases, the temperature increases to reach a stable value. At the nozzle, the temperature ranges from 395 K to a stable value of 409 K, and at 12 mm from the nozzle the temperature ranges from 376 to 380 K.  
As shown in Figures 9 and 10, the gas temperatures of the plume in O\({}_{2}\)/Ar admixtures (with 1 slm of argon flow rate) are slightly lower than those in pure argon discharges. However, as the oxygen ratio increases, the temperature begins to increase and then becomes stable. The reason for this difference between the temperatures of Ar/O\({}_{2}\) and Ar plasmas might be because, as the oxygen ratio increases, the numbers of collisions among particles increase with the flow rate, and more particles participate in energy exchange and dissipating power processes [32]. Therefore, the rotational temperature and vibrational temperature decrease as a result of processes that occur due to adding oxygen to the argon during discharge. Furthermore, adding oxygen accelerates the disinfection process, since a large quantity of thermal energy is transferred from the jet to the alive culture compared with the case for pure argon--the thermal conductivity of oxygen (0.0238 W m\({}^{-1}\) K\({}^{-1}\)) is higher than that of argon (0.0162 W\(\cdot\)m\({}^{-1}\) K\({}^{-1}\)) [33].