The effect of air admixture in the argon flow on ozone absorption in a time modulated atmospheric pressure plasma jet

Ozone produced by the atmospheric pressure plasma jet has attracted great interests because of its compact size and wide area of applications. The ozone can be used to disinfect, sterilize, heal wounds, kill bacteria, and clean water. The plasma jet operates with the flow of noble gas, such as argon in this work. To produce ozone efficiently, molecular oxygen is a common admixture, like in helium-oxygen capillary DBD, or argon-oxygen plasma jet. Air is also another admixture in the noble gas because air is much easier to obtain and much more abundant. In some cases, air is the only fed gas. After the air is added into the argon, the reactive species change greatly due to the occurrence of nitric species. In \cite{winter2012aspects}, Winter {\it et al} studied the absorption signal in an Ar+O$_2$ plasma jet for different background gases, pure oxygen, synthetic air and pure nitrogen respectively in a chamber in the UV range and the infrared range and verified that the background gas of air has little effect on ozone absorption of UV light. However, the air entrainment is negligible in the plasma core zone. Consequently the produced nitric species due to air entrainment in the core zone is also ignored. In this work, the plasma jet is fed argon gas with premixed air to investigate the effect of nitric species on the absorption of UV by ozone.