Influence of a liquid surface on the NOx production of a cold atmospheric pressure plasma jet

In this work a cold atmospheric pressure plasma jet was mounted above a distilled water reservoir to study the influence of a water surface on reactive oxygen and nitrogen species (RONS) generation. The RONS, namely O-3 and NO2, were measured by multi-pass cell Fourier transform infrared absorption spectroscopy in the far-field of the jet. A shielding gas device was used to control the ambient environment of the effluent. The liquid surface has nearly no influence on the RONS dynamics as a function of shielding gas composition. It was found, however, that the interaction with the liquid surface increases the density of NOx by a factor of 2-3 due to local increase in H2O concentration through evaporation of water from the liquid surface. In contrast to the case of ambient humidity increase, this locally higher H2O density distinctly influences the ratio of water to oxygen and nitrogen which results in a higher generation of OH molecules.