# Ozone Generation by Surface Dielectric Barrier Discharge
## 3 Results and Discussion
### Ozone Concentration Indoors  
Finally, we studied the temporal variation of the ozone concentration in the room (with a volume of 60 m\({}^{3}\)) in which the SDBD generator was working. Since, as was shown in the previous subsection, the ozone production for all three generator types can be characterized by one parameter--ozone production efficiency, which we tested on only one generator--with a smooth-edge electrode for various active powers (Figure 8), and the conclusions can be extended to the other generators. In Figure 8, the SDBD was turned on at time t = 0 and turned off after 2.5 h of operation. We registered the increase in the ozone concentration during the operation of the generator, and next its decrease after turning it off, as the ozone decomposed until its concentration in the room dropped to 0 ppm. After the generator is switched on, the concentration of ozone in the room increases until an equilibrium state is reached in which the amount of ozone generated in the SDBD discharge is balanced by the amount of ozone being decomposed, mainly through recombination in collisions with air molecules and unimolecular decay [65; 66; 67]. When the SDBD is turned off, the ozone concentration starts to decrease, since the decomposition processes become dominant. In the studied case, the equilibrium state was reached about 1.5 h after the generator was turned on. In this timeframe, the ozone concentration can be expressed as a function of time using Equation (1):  
\[C(t)=C_{e}\Big{(}1-e^{-\frac{t}{t}}\Big{)} \tag{1}\]  
where \(C_{e}\)--ozone concentration is in the equilibrium state, \(\tau\)--ozone production growth factor [40]. Similarly, the ozone concentration over time, after the generator was turned off, can be expressed using Equation (2):  
\[C(t)=C_{e^{\prime}}e^{-\frac{t-t_{off}}{\tau^{\prime}}} \tag{2}\]  
where \(C_{e^{\prime}}\)--initial ozone concentration, \(\tau^{\prime}\)--ozone decomposition growth factor, \(t_{off}\)--time at which the SDBD was turned off (in the studied case \(t_{off}\) = 2.5 h) [40; 68]. The approximation function is shown with the solid lines in Figure 8, and as can be seen, the data points are reasonably well approximated with the functions described by Equations (1) and (2). The  
Figure 7: Ozone production yield as a function of the active power dissipated in the SDBD for three types of generators. The dashed line is the linear fit for all three sets of data points. approximation parameters and the ozone half-life time calculated for the decomposition phase (T\({}_{1/2}\)) can be found in Table 1.  
The average ozone production and decomposition growth factors are \(\tau\) = 0.476 \(\pm\) 0.08 h and \(\tau^{\prime}\) = 0.332 \(\pm\) 0.07 h, respectively, and the ozone half-life time varies from 10.4 min to 15.8 min. A similar ozone half-life time of 16 min was recently reported by [PERSON] et al. [69], which studied the ozone decomposition generated by a household dryer in a closed room. [PERSON] et al. [70] reported ozone half-life time ranging from approximately 30 min to 60 min, and [PERSON] [71] from 6 min to 40 min, depending on the indoor environment. Using the approximation parameters (Table 1), the maximal ozone concentration in the room in the equilibrium state (\(C_{e}\)) can be expressed as a function of the active power (Figure 9). As expected, the maximal ozone concentration in the room is the linear function of the active discharge power, which can be extended for all three types of generators.