On the Role of Metastable Argon in Cold Atmospheric Pressure Plasma Jets with Shielding Gas Device*

Shielding gas devices are a valuable tool for controlling the reactive species output of Cold Atmospheric Pressure Plasma (CAPP) Jets for biomedical applications. In this work we investigate the effect of different shielding gas compositions using a CAPP jet (kinpen) operated with argon. As shielding gas various mixtures of N$_{2}$ and O$_{2}$ are used. Metastable argon (Ar*) has been quantified using laser absorption spectroscopy and was identified as an important energy carrier in the CAPP jets effluent. The Ar* excitation dynamics was studied using phase resolve optical emission spectroscopy. Based on these findings a kinetic model for the gas phase chemistry has been developed that uses the Ar* density and dynamics as input and yields densities of O$_{3}$, NO$_{2}$, HNO$_{2}$, HNO$_{3}$, N$_{2}$O$_{5}$, H$_{2}$O$_{2}$ and N$_{2}$O produced by the CAPP jet for different shielding gas compositions. The results are in good agreement with Fourier-Transform Infrared Spectroscopy measurements on these species.