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The influence of the addition of O2 on the OH production in a He + 0.1 % H2O discharge is investigated using laser induced fluorescence. The plasma properties $$(T_{\rm g},\;n_{\rm e})$$ are reported and used to explain the observed time and spatially resolved OH density, which is absolutely calibrated using Rayleigh scattering. Compared to the case when only H2O is added, an increase in the measured OH density is observed in the far afterglow. A zero-dimensional chemical kinetic model is constructed, which allows to determine the reactions responsible for the OH production in the far afterglow. When O2 is admixed, the key reaction $$\hbox{O} + \hbox{OH} \longrightarrow \hbox{O}_{2} + \hbox{H}$$ causes quenching of OH and production of increased densities of H, HO2 and H2O2, which subsequently leads to additional OH production in the late afterglow.

Summary form only given. During the last decade non-thermal (multiphase) atmospheric pressure plasmas have received a tremendous increase of attention in view of their potential in biomedical, chemical, environmental and material processing applications.

Summary form only given. Atmospheric pressure plasmas are investigated more and more in view of environmental en biomedical applications. One of the active species that are important for applications such as air cleaning is the OH radical1. This radical is ubiquitous in the water containing air plasmas and is very efficient due to its high oxidation potential.

International audience; Absolute OH densities are obtained in a radio-frequency-driven Ar-H2O atmospheric-pressure plasma jet by laser-induced fluorescence (LIF), calibrated by Rayleigh scattering and by UV broadband absorption. The measurements are carried out in ambient air and the effect of air entrainment into the Ar jet is measured by analyzing the time-resolved fluorescence signals. The OH densities are obtained for different water vapor concentrations admixed to the Ar and as a function of the axial distance from the nozzle. A sensitivity analysis to deduce the accuracy of the model-calculated OH density from the LIF measurement is reported. It is found that the UV absorption and the LIF results correspond within experimental accuracy close to the nozzle and deviate in the far effluent. The possible reasons are discussed. The OH densities found in the plasma jet are in the range (0.1-2.5) × 1021 m-3 depending on the water concentration and plasma conditions.

A set of diagnostic methods to obtain the plasma parameters including power dissipation, gas temperature and electron density is evaluated for an atmospheric pressure helium or argon radio frequency (RF) plasma needle for biomedical applications operated in open air. The power density of the plasma is more or less constant and equal to 1.3 ? 109?W?m?3. Different methods are investigated and evaluated to obtain the gas temperature. In this paper the gas temperatures obtained by rotational spectra of OH(A?X) and (B?X) are compared with Rayleigh scattering measurements and measurements of the line broadening of hydrogen and helium emission lines. The obtained gas temperature ranges from 300 to 650?K, depending on the gas. The electron densities are estimated from the Stark broadening of the hydrogen ? and ? lines which yield values between 1019 and 1020?m?3. In the case of helium, this is an overestimate as is shown by a power balance from the measured power density in the plasma jet. The obtained plasma parameters enable us to explain the radial contraction of the argon plasma compared with the more diffuse helium plasma. The accuracy of all considered diagnostics is discussed in detail.