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In this paper we use a (sub)nanosecond high-voltage pulse source (2–9 ns pulses with 0.4 ns rise time) to generate streamer plasma in a wire-cylinder reactor and apply it to two atmospheric plasma processing applications: ozone generation and NO removal. We will investigate what pulse parameters result in the highest plasma processing yields.The results show that for ozone generation, secondary-streamer effects appear to have a slight influence on the ozone yield: if the pulse duration increases and/or the voltage increases in such a way that streamers can start to cross the gap in the reactor, the ozone yields decrease. Furthermore, for NO removal, we see a similar effect of pulse duration and applied voltage as for the ozone generation, but the effect of the pulse duration is slightly different: long pulses result in the highest NO-removal yield. However, the NO-removal process is fundamentally different: besides removing NO, the plasma also produces NO and this production is more pronounced in the primary-streamer phase, which is why the pulse polarity has almost no influence on the NO-removal yield (only on the by-product formation). Moreover, the rise time of the pulses has a much more significant effect on ozone generation and NO removal than the pulse duration: a long rise time results in a lower enhanced electric field at the streamer heads, which consequently reduces the production of radicals required for ozone generation and NO removal, and decreases the streamer volume. Consequently, the resulting ozone yields and NO-removal yields are lower. Finally, the main conclusion is that the plasma generated with our nanosecond pulses is very efficient for ozone generation and NO removal, achieving yields as high as 175 g centerdot ${\rm kWh}^{-1}$ for ozone generation and 2.5 mol centerdot ${\rm kWh}^{-1}$ (or 14.9 eV per NO molecule) for NO removal.

The oxidative degradation of two volatile organic compounds, i.e. toluene (fossil fuel based VOC) and limonene (biogenic VOC), has been studied. A hybrid pulsed power corona reactor with adjustable energy density has been utilized for degradation of ppm level target compounds in large air flows. The observed oxidation product range features an energy density-dependent spectrum of oxygen-functional hydrocarbons, which has been qualitatively discussed on the basis of literature studies. Typically, observed stable oxidation products for both target compounds are the biocompatible carboxylic acids acetic and formic acid. Measured degradation G-values are 23 nmol J-1 at 74% conversion of 70 ppm toluene and 181 nmol J-1 at 81% conversion of 10 ppm limonene.

A new method for the removal of harmful organic molecules from water is described. A low power corona discharge is created over the aqueous solution. Chemically active species diffuse into the water and then oxidize the target compound, which in this case is the model compound phenol. The energy consumption per removed phenol molecule is one order of magnitude lower compared to the discharge techniques that create a plasma in the water. The reaction mechanism of the conversion is shown by measuring the ozone concentration over the water, the intermediate/final oxidation products and the release of CO2 from the water. Indications are found that the discharge is more than merely an ozone generator.

LIF spectroscopy has been introduced for the in situ diagnostic of phenol degradation in the aqueous solution under pulsed-corona discharges. The applicability of LIF to the measurements of phenol concentration up to 1 × 10-5 mol l-1 was confirmed. The temporal variation of the absolute concentration of phenol was measured in an aqueous solution exposed by pulsed-corona discharges. This exhibited two characteristic decay times.

In this paper we investigate temperature and pressure effects on the properties of a positive pulsed streamer plasma. We use a corona plasma setup in which we vary the temperature between 303 and 773K at atmospheric pressure and the pressure between 37.9 and 100 kPa at room temperature to achieve the same neutral gas density and compare electrical and optical (ICCD imaging) measurements carried out in both experiments. From the measurements we found that the dissipated plasma energy and the average streamer propagation velocity are both higher for the temperature experiments at the same neutral gas densities as in the pressure experiments. This suggests the existence of a specific temperature effect. A possible explanation for this effect is a higher streamer conductivity at high temperatures, as was previously found in the literature.