# Ozone Generation by Surface Dielectric Barrier Discharge
## 3 Results and Discussion
### Ozone Production Yield  
In a very simplified form, the formation of ozone in the DBD discharge in the air can be represented as a two-step process. In the first step, the free charges generated in the discharge collide with oxygen molecules, which results in their dissociation into their constituent oxygen atoms (e + O\({}_{2}\rightarrow\) e + O + O). The next step is a three-body reaction of one of these oxygen atoms with the oxygen molecules and another air molecule (usually oxygen or nitrogen) which leads to the formation of the ozone molecule (O + O\({}_{2}\) + M \(\rightarrow\) O\({}_{3}\) + M). For a more detailed description of the plasma chemistry that leads to the formation of ozone and other oxygen and nitrogen species, see [11; 15; 62; 63]. Figure 6 shows the ozone production yield as a function of the applied voltage for all three generator types. One has to keep in mind that the results presented in this paper are for a fixed electrode length (75 mm); however, as was shown by [PERSON] et al. [40], the ozone production yield is a linear function of the electrode length. As expected, the ozone yield increases with increasing applied voltage in all studied cases. This is understandable since an increase in the applied voltage increases the number and energy of free charges, which promotes  
Figure 5: Typical time-resolved images of the SDBD plasma in the various time windows for three types of generators. Applied voltage V\({}_{\rm pp}\) = 18.5 kV, exposure time—40 \(\upmu\)s.  
oxygen dissociation and the following three-body collision process. For a given value of applied voltage, the production yield from the generator with a smooth-edge and serrated electrode is similar, reaching maximally 46 mg/h and 44 mg/h, respectively, for 21.6 kV and is significantly lower for the one with the thin-wire electrode reaching maximally 36.3 mg/h. It can be assumed that the reduction of the ozone yield for the thin-wire electrode generator is due to discharge inhibition, which was experimentally confirmed in this research and is discussed in Sections 3.1-3.3.  
Using the results of the active power measurements discussed in Section 3.2, in Figure 7, the ozone production yield is shown as the function of discharge active power. As can be seen, the data points of all three series, corresponding to the three types of generators, line up along a single, straight line, and were fitted with a linear function (marked with a dashed line in the graph). This suggests that although the ozone production yield varies with the electrode geometry and applied voltage, the ozone production efficiency can be expressed as a function of a single dependent parameter--the active discharge power. From the slope of the approximation function in Figure 7, we calculated the ozone production efficiency of the generators to be 9.66 g/kWh. This value is about 2 times smaller than the 21.2 g/kWh obtained by [PERSON] et al. (2010) from their SDBD actuator with a serrated electrode and 3 mm electrode gap, which is to our knowledge the smallest value obtained for an SDBD reactor. In comparison, [PERSON] et al. (2014) developed an SDBD plasma reactor for ozone generation, achieving a much higher energy efficiency of 52 g/kWh. Using an SDBD in a multi-electrode configuration, [PERSON] et al. (2010) obtained an efficiency of 131 g/kWh by optimizing the airflow in the reaction chamber. The relatively low ozone production efficiency of the generators in our studies is an advantage for our purposes, as it potentially allows it to be used in the vicinity of people.  
Figure 6: Ozone production yield as a function of applied voltage for three types of generators.