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Abstract Enhancing mass transport of reactive species and photons at the plasmaliquid interface is an important consideration for the scaling of atmospheric pressure plasmas studied in the laboratory to real-world applications. It is well-known that the introduction of turbulence at any interface will enhance mixing by enhancing species uptake from the gas phase to the liquid phase by surface renewal processes, entrainment, bubbles and surface area modification. The goal of this work is to isolate surface effects associated with turbulence from the multitude of turbulent transport enhanced processes by artificially introducing surface perturbations using Faraday waves. Experiments were also conducted to determine decoloration rate constants of a model contaminant (methylene blue) as a function of both discharge features and hydrodynamics (Faraday surface wavelengths). The local plasma ionization wave at the interfacial structure was modeled and compared to experiments. Interestingly, it was found in experiments that plasma in contact with the water also generated capillary waves thus modifying the surface as well. Plasma ionization waves in combination to acoustic driven Faraday waves adds to the complexity of interpreting the effects of, for example, surface area increases, due to these complex coupled phenomenon. Local plasma ionization wave structure appears to be modified (increased propagation distance) when the liquid is perturbed, leading to increased contact of the liquid water surface with reactive species. Along with interfacial surface area growth, nonlinear convective transport is also increased with perturbations, leading to the general realization that acoustic perturbations can improve transport and thus decoloration of the model contaminant dye. 

Abstract In an atmospheric DC glow discharge with liquid anode, the plasma attachment under certain conditions self-organize into coherent patterns at the anode. Optical emission spectroscopy revealed that attachment emission consists primarily of the second positive system of nitrogen N2(C-B) whose excitation energy is low and sensitive to the change of electron energy distribution. Besides the electrons, negative ions can also accumulate in the anode sheath and affect the local space charge. It has been conjectured that these negative ions play a role in pattern formation at the anode surface. In this work, the role of oxygen negative ions was explored. It was found that the establishment of anode patterns requires at least a 7 % volume fraction of oxygen in the ambient gas. Results showed that at least in this work, O2- is the dominant negative ion species and has a density ~10^13 cm^-3. While the presence of oxygen appears crucial to pattern formation, this study indicated that the mere presence of the negative ions itself was not sufficient for pattern formation, suggesting a more complex mechanism involving electronegative species must be present. In fact, it was found that even when as many as 67 % of negative ions in the plasma were detached, no obvious geometry changes were observed in the self-organized pattern.