A kinetic simulation of various neutral species created by the corona effect in dry or humid oxygen is presented. The physical conditions of the pulsed electrical discharge used are: atmospheric pressure, a gas discharge channel temperature in the 200 to 800 K range and an electron density Ne=5*1015 cm-3 or 1016 cm-3 with the electron energy assumed to be larger than 5 eV. The presence of water vapour leads to a non-negligible H2O2 production. Temperature and humidity have a cumulative effect on the O3 production. With multiple pulses, the maximal O3 concentration is obtained for a finite number of pulses.

Plasma chemistry at atmospheric pressure and low temperature has met an increased interest due to the effective production of reactive species (mainly reactive nitrogen species and reactive oxygen species) which are demanded in many applications like in biomedicine. Τhe generation of such emissive reactive species is herein studied. A single parameter, i.e., the gas composition, is tuned and abundant chemical species are obtained in a quite controllable manner. The system refers to a small dielectric barrier discharge based reactor fed with He–N2/O2 or Ar–N2/O2 gases, which provides plasma in the form of “guided streamers.” The plasma is sustained by positive high voltage pulses, and the emissive transitions versus the gas composition is determined by UV-VIS optical emission spectroscopy. The relative intensities of emissive species are recorded in the ambient air where the streamers propagate. The evolution of dominant species as a function of the gas composition is mapped, and optimal conditions in terms of species production are clearly revealed. The results show that additives do not necessarily enhance the density of all species, implying the need for plasma chemistry optimization in respect to every application. The study is extended inside the reactor, supporting the above statements. Finally, the rotational and vibrational distributions of critical probe molecules are recorded, testing the dependence of the gas temperature and energy transfer, respectively, on the gas composition.

The understanding of plasma-liquid interactions is of major importance, not only in physical chemistry, chemical engineering and polymer science, but in biomedicine as well as to better control the biological processes induced on/in biological samples by Cold Atmospheric Plasmas (CAPs). Moreover, plasma-air interactions have to be particularly considered since these CAPs propagate in the ambient air. Herein, we developed a helium-based CAP setup equipped with a shielding-gas device, which allows the control of plasma-air interactions. Thanks to this device, we obtained specific diffuse CAPs, with the ability to propagate along several centimetres in the ambient air at atmospheric pressure. Optical Emission Spectroscopy (OES) measurements were performed on these CAPs during their interaction with a liquid medium (phosphate-buffered saline PBS 10 mM, pH 7.4) giving valuable information about the induced chemistry as a function of the shielding gas composition (variable O2/(O2 + N2) ratio). Several excited species were detected including N2+(First Negative System, FNS), N2(Second Positive System, SPS) and HO˙ radical. The ratios between nitrogen/oxygen excited species strongly depend on the O2/(O2 + N2) ratio. The liquid chemistry developed after CAP treatment was investigated by combining electrochemical and UV-visible absorption spectroscopy methods. We detected and quantified stable oxygen and nitrogen species (H2O2, NO2-, NO3-) along with Reactive Nitrogen Species (RNS) such as the peroxynitrite anion ONOO-. It appears that the RNS/ROS (Reactive Oxygen Species) ratio in the treated liquid depends also on the shielding gas composition. Eventually, the composition of the surrounding environment of CAPs seems to be crucial for the induced plasma chemistry and consequently, for the liquid chemistry. All these results demonstrate clearly that for physical, chemical and biomedical applications, which are usually achieved in ambient air environments, it is necessary to realize an effective control of plasma-air interactions.

A numerical simulation including kinetics, transport phenomena and temperature gradient is presented to describe axial and radial distribution of ozone in an oxygen-fed ozonizer with cylindrical symmetry. The interdependence of three types of modelling (kinetics, hydrodynamics and electronic injection due to electrical corona discharge) is emphasized and comparisons are made with previous simpler models. The simulation is performed in the case of an industrial cylinder-to-cylinder device for which the temperature gradient is negligible, and in the case of a laboratory wire-to-cylinder ozonizer where an important radial temperature gradient is experimentally observed. Two values of pressure are considered: 760 Torr, where chemical kinetics dominates over diffusion effects, and 10 Torr where diffusion is dominant.