Based on numerical modelling and physical understanding of plasma jets, dissociation can be controlled by considering the following factors

1) The Ozone decomposition depends specifically on the temperature of gas that can be controlled by the effect of gas flow rate.

2) The proper control of impurities can also effect on the dissociation of ozone at atmospheric pressure plasma jets in the mentioned frequency regime of question.

3) Apply the external imposed potential greater than the breakdown voltage at the specific gap spacing.

In my opinion, chapter 6 provides a better understanding in this regarding ozone dissociation of the book

A. Fridman, Plasma Chemistry, Cambridge University Press, New York, ISBN-13 978-0-521-84735-3 hardback, 2008.

Good luck

Munawar

I once worked in a laboratory where the concentration of ozone produced by a cylindrical DBD was studied as a function of frequency and flow rate, two important parameters, and it was verified that there exist a frequency where the production of ozone is maximum, for a given fixed flow rate. This probably depends on the system and particular geometry. One could, for example, set a frequency well beyond this maximum value in order to avoid ozone production. One should have in mind that ozone is formed in the off phase of the plasma, where the dissociated oxygen species react to form ozone. If this period of the off phase is shortened (i.e, the frequency is increased), the ozone density will decrease.    

I studied theoretically the ozone density as a function of the flow rate and compared it with experimental result. The ozone density decreases monotonically with flow rate, but the total throughput increases and then saturates.

It probably does not entirely answer the question, but I hope it could give some glimpses on how to avoid O3 production in plasmas jets.  

Is it possible to use another gas for the discharge such as argon or helium? We use argon to avoid ozone formation in our plasma discharges. The ozone is formed from oxygen gas. We are currently measuring the ozone using indigo dye.

Yes Kevin, it is not just possible, but preferable in order to avoid ozone formation. Actually, it is much easier to ignite a plasma jet in helium and argon (particularly in argon), tough it is possible do produce a plasma jet of nitrogen or/and oxygen. Nevertheless, some oxygen (O2) intrusion may occur anyway and ozone may form even when the feed gas is argon or helium.