An atmospheric pressure surface-wave microwave discharge and a kHz plasma jet are used to activate purified water. It is shown, that by varying the treatment distance and the initial Ar/N 2 /O 2 mixture composition of the surface-wave microwave discharge the concentration ratio of NO 3 − and H 2 O 2 radicals created in the plasma activated water (PAW) can be varied over three orders of magnitude, which can be preserved during months of storage at room temperature. At the same time, with the 5min treatment of the 32ml water the absolute radical concentrations are varied in the range of 0.5-85mg l −1 for H 2 O 2 , 20-180mg l −1 for NO 3 − and 0.5-14mg l −1 for NO 2 −. In the case of the N 2 kHz plasma jet this concentration ratio can be tuned within one order of magnitude by varying the treatment distance. By treating different volumes very similar concentration ratios are obtained, which evolve differently during storage, as the ageing dynamics is determined by the absolute concentration of radicals. In general, the radical most affected by ageing is NO 2 − , whose recombination is found to be determined by the H 2 O 2 radical. In order to control the H 2 O 2 concentration and thus the NO 2 − radicals recombination, the application of a Fenton type reaction is suggested, which is implied by inserting a copper surface into PAW during or after plasma treatment.

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A study on oxygen-plasma treatment of ink-jet paper is presented. Paper was exposed to a weakly ionized, highly dissociated oxygen plasma with an electron temperature of 5 eV, a positive-ion density of 8 × 1015 m−3 and a density of neutral oxygen atoms of 5 × 1021 m−3. Optical emission spectroscopy (OES) was applied as a method for detection of the reaction products during the plasma treatment of the paper. OES spectra between 250 and 1000 nm were measured continuously during the plasma treatment. The wettability of the samples before and after the plasma treatment was determined by measuring the contact angle of a water drop. The appearance of the surface-functional groups was determined by using high-resolution x-ray photoelectron spectroscopy (XPS), while changes in the surface morphology were monitored with scanning electron microscopy (SEM). Already after 1 s of the plasma treatment the surface, which was originally hydrophobic, changed to hydrophilic, as indicated by a high absorption rate of a water drop into the paper. The OES showed a rapid increase of the CO and OH bands for the first few seconds of the plasma treatment, followed by a slow decrease during the next 40 s. The intensity of the O atom line showed reversed behaviour. The XPS analyses showed a gradual increase of oxygen-rich functional groups on the surface, while SEM analyses did not show significant modification of the morphology during the first 10 s of the plasma treatment. The results were explained by degradation of the alkyl ketene dimer sizing agent during the first few seconds of the oxygen-plasma treatment.

Optical emission spectroscopy (OES) analysis of inductively coupled RF oxygen plasma during plasma treatment of a 23 µm thick polyethylene terephthalate (PET) foil is presented. Plasma was generated in pure oxygen at a pressure of 75 Pa with a RF generator at a frequency of 27.12 MHz and an output power of 300 W. The electron temperature was about 6 eV, the density of charged particles about 1016 m−3 and the density of neutral O atoms about 1022 m−3. Spectra were measured in the range from 250 to 950 nm by means of an optical spectrometer. For the first 10 s of plasma treatment the OES showed the presence of oxygen radicals only. Later, the OES spectra became richer with significant emission from CO and OH, which was attributed to PET oxidation. Simultaneously, the O peaks decreased significantly. After prolonged plasma treatment, the O peaks recovered, the CO band vanished while the OH and H peaks still persisted. In the final period of the treatment only atomic oxygen lines remained. The results showed that OES analysis was a powerful method for studying the evolution of PET oxidation by plasma treatment.

Pulsed cavity ring-down spectroscopy (CRDS) is a direct absorption, highly sensitive, versatile technique suitable for the analysis of a wide range of plasmas. CRDS belongs to a wide class of cavity-enhanced spectroscopies. This work briefly describes the basic principles of CRDS and summarizes the main literature specifically related to applications for atmospheric pressure plasma jets (APPJ). Emphasis is given to the temporal resolution and pulsed character of the plasma sources. As an example we present in more detail the determination of metastable helium density in the 2s S 3 1 state produced in a single-electrode atmospheric pressure plasma jet driven by a pulsed high-voltage waveform. Measured He( S 3 1 ) number densities ranged from × −