## 3 Results and Discussion
### Possible Reactions in the Interaction of DBD Plasmas and Water Molecules  
Despite the type of gas species used during the treatment with considering the electron temperature that is around 1 eV for all DBD plasmas, the collision of electrons with water molecules might provide the following reactions [26]:  
\[\mathrm{e}+\mathrm{H_{2}O}\rightarrow\mathrm{OH\bullet}+\mathrm{H+e} \tag{2}\]  
\[\mathrm{e}+\mathrm{H_{2}O}\rightarrow\mathrm{H_{2}O^{\bullet}+e} \tag{3}\]  
\[\mathrm{e}+\mathrm{H_{2}O^{\bullet}\rightarrow\mathrm{H_{2}O^{+}+2e}} \tag{4}\]  
\[\mathrm{H_{2}O+H_{2}O^{+}\rightarrow\mathrm{OH\bullet}+H_{3}O^{+}} \tag{5}\]  
In addition, the water molecule is dissociated by the following reaction:  
\[\mathrm{H_{2}O+M^{\bullet}\rightarrow\mathrm{OH\bullet}+H+M} \tag{6}\]  
where M represents the excited species as shown in Reactions 9, 13, and 18.  
In addition to the above reactions, in the case of argon DBD plasma, the excited atoms formed in the gas phase in interaction with water molecules generate hydroxyl radicals [27].  
\[\mathrm{Ar+e}\rightarrow\mathrm{Ar^{+}+e+e} \tag{7}\]  
\[\mathrm{Ar+e}\rightarrow\mathrm{Ar^{\bullet}+e} \tag{8}\]  
\[\mathrm{Ar^{\bullet}+H_{2}O}\rightarrow\mathrm{Ar+OH\bullet+H} \tag{9}\]  
In the case of oxygen plasmas, produced excited oxygen species, and then in interaction with water molecule give the following reactions [28]:  
\[\mathrm{O_{2}+e}\rightarrow\mathrm{O^{+}+O+2e} \tag{10}\]  
\[\mathrm{O_{2}+e}\rightarrow\mathrm{O^{-}+O} \tag{11}\]  
\[\mathrm{O+O_{2}\rightarrow\mathrm{O_{3}}} \tag{12}\]  
\[\mathrm{O+H_{2}O}\rightarrow\mathrm{2\ OH\bullet} \tag{13}\]  
\[\mathrm{O_{3}+OH^{-}\rightarrow\mathrm{HO_{2}}^{-}+O_{2}} \tag{14}\]  
\[\mathrm{O_{3}+HO_{2}}^{-}\rightarrow\mathrm{OH\bullet+O_{2}}^{-}+O_{2} \tag{15}\]  
The following procedures occur in the gas phases of nitrogen DBD plasmas [28].  
\[\mathrm{e}+\mathrm{N_{2}\rightarrow\mathrm{N+N+e}} \tag{16}\]  
\[\mathrm{e}+\mathrm{N_{2}\rightarrow\mathrm{N_{2}}^{\bullet}+e} \tag{17}\]  
\[\mathrm{N^{\bullet}+H_{2}O}\rightarrow\mathrm{N+OH\bullet+H} \tag{18}\]\[\mathrm{N^{*}+H_{2}O\rightarrowOH\bullet NH} \tag{19}\]  
\[\mathrm{N_{2}^{*}+H_{2}O\rightarrowN_{2}+H+OH\bullet} \tag{20}\]  
\[\mathrm{H_{2}O+}\mathit{hv}\rightarrow\mathrm{OH\bullet+H} \tag{21}\]  
In addition to Reactions 10-20, the following reactions in the gas phase of air DBD plasmas are also included:  
\[\mathrm{e+N_{2}+O_{2}\rightarrow2N+2O+e} \tag{22}\]  
\[\mathrm{N+O\rightarrowNO\bullet} \tag{23}\]  
\[\mathrm{N+O_{2}\rightarrowNO\bullet}+O \tag{24}\]  
\[\mathrm{O+N_{2}\rightarrowNO\bullet+N} \tag{25}\]  
\[\mathrm{H_{2}O+}\mathit{hv}\rightarrow\mathrm{OH\bullet+H} \tag{26}\]  
Excited molecular nitrogen (\(\mathrm{N_{2}^{*}}\)) in Reaction 17 as well as nitric oxide radical (NO) in Reactions 23-25 can be observed in the nitrogen and air spectra (Figure 3c,d) in the wavelength range of 280 to 450 nm. However, excited atomic nitrogen was not observed in the spectra as the wavelength range is less than 200 nm [29]. This range which relies on the vacuum ultraviolet (VUV), is out of the wavelength range of our spectrometer. As shown in the nitrogen and air spectra (Figure 3c,d), both DBD plasmas generate nitric oxide radicals. It is known that the air DBD generates nitric oxide radical because of Reactions 23-25. In the case of nitrogen DBD, after generating NH species by Reaction 19, nitric oxide radicals can be generated by the following reaction [28]:  
\[\mathrm{NH+OH\bullet\rightarrowH_{2}+NO\bullet} \tag{27}\]  
Besides, the hydroxyl radicals are quenched by interacting with active nitrogen species in the gas phase [30]. That is the reason the wavelength peak of hydroxyl radical is not observed in the nitrogen and air spectra (Figure 3c,d). Nevertheless, the hydroxyl radical might be produced in nitrogen and air DBD plasmas due to Reactions 18-20, and 26.