This contribution investigates the effects of duty cycle and mass flow of synthetic air and oxygen on the efficiency of ozone generation in multi-hollow surface dielectric barrier discharge (MSDBD). It discloses that the efficiency of ozone generation in MSDBD is significantly higher compared with standard coplanar DBD, surface DBD and volume DBDs. Ozone production yield reached 205.5 ± 29.1 g (kW h) ⁻¹ (40% duty cycle, 8 slm) and 413.91 ± 58.7 g (kW h) ⁻¹ (100% duty cycle, 8 slm) at an energy cost of 8.7 and 4.3 eV/molecule for synthetic air and oxygen, respectively. Such high ozone yields arose out of the intrinsic characteristics of MSDBD ceramics, which were efficiently cooled by the flow of the working gas. The amplitude modulation of low-frequency 5 kHz high-voltage sine waveforms facilitates controlled O ₃ production at a nearly constant rate of yield. Since the correct evaluation of ozone production yield requires precise determination of the discharge power, the concentration of ozone and working gas-flow, considerable attention was paid to measurements of these parameters. It is confirmed and experimentally demonstrated herein that correct determination of discharge power lies with Lissajous figure methods, while the determination of power through the direct integration of product u ( t ) i ( t ), where i ( t ) is measured by Pearson current probe, leads to systematically lower values of calculated power with consequent overestimation of the ozone production yield. The correct determination of discharge power is clearly the key to the proper calculation of ozone production yield and efficiency. Under the DBD discharge conditions presented herein, ozone production yield and efficiency achieved figures as high as 19.5% and 35.2% of theoretical limits recently established for air and oxygen, respectively.

Naturally contaminated basil seeds were treated by a surface dielectric barrier discharge driven in the humid air by an amplitude modulated AC high voltage to avoid heat shock. In order to avoid direct contact of seeds with microdischarge filaments, the seeds to be treated were placed at sufficient distance from the surface discharge. After treatment, the seeds were analyzed in comparison with control samples for their microbial contamination as well as for the capability of germination and seedling growth. Moreover, chemical modification of seed surface was observed through the elemental energy dispersive x-ray analysis and wettability tests. We found that treatment applied at 20% duty cycle (effective discharge duration up to 20 s) significantly decreases microbial load without reducing the viability of the seeds. On the other side, seedling growth was considerably accelerated after the treatment, and biometric growth parameters of seedlings (total length, weight, leaf extension) considerably increased compared to the controls. Interestingly, scanning electron microscopy images taken for the different duration of treatment revealed that seed radicle micropylar regions underwent significant morphological changes while the coat was substantially undamaged. Inside the seed, the embryo seemed to be well preserved while the endosperm body was detached from the epithelial tegument. A total of 9 different genera of fungi were recovered from the analyzed seeds. Scanning electron microscopy images revealed that conidia were localized especially in the micropylar region, and after plasma treatment, most of them showed substantial damages. Therefore, the overall effect of the treatment of naturally contaminated seeds by reactive oxygen and nitrogen species produced by plasma and the consequent changes in surface chemistry and microbial load can significantly improve seed vigor.

Many studies proved that non-equilibrium discharges generated at atmospheric pressure are highly effective for the bio-decontamination of surfaces of various materials. One of the key processes that leads to a desired result is plasma etching and thus the evaluation of etching rates of organic materials is of high importance. However, the comparison of reported results is rather difficult if impossible as different authors use diverse sources of atmospheric plasma that are operated at significantly different operational parameters. Therefore, we report here on the systematic study of the etching of nine different common polymers that mimic the different structures of more complicated biological systems, bovine serum albumin (BSA) selected as the model protein and spores of Bacillus subtilis taken as a representative of highly resistant micro-organisms. The treatment of these materials was performed by means of atmospheric pressure dielectric barrier discharge (DBD) sustained in open air at constant conditions. All tested polymers, BSA and spores, were readily etched by DBD plasma. However, the measured etching rates were found to be dependent on the chemical structure of treated materials, namely on the presence of oxygen in the structure of polymers.

The initial stages of transient luminous events (TLEs) occurring in the upper atmosphere of the Earth are, in a certain pressure range, controlled by the streamer mechanism. This paper presents the results of the first laboratory experiments to study the TLE streamer phenomena under conditions close to those of the upper atmosphere. Spectrally and highly spatiotemporally resolved emissions originating from radiative states N 2 ( C 3 Π u ) (second positive system) and N 2 + ( B 2 Σ u + ) (first negative system) have been recorded from the positive streamer discharge. Periodic ionizing events were generated in a barrier discharge arrangement at a pressure of 4 torr of synthetic air, i.e. simulating the pressure conditions at altitudes of ≃37 km. Employing Abel inversion on the radially scanned streamer emission and a 2D fitting procedure, access was obtained to the local spectral signatures within the over 10 ⁶ m s ⁻¹ fast propagating streamers. The reduced electric field strength distribution within the streamer head was determined from the ratio of the N 2 + / N 2 band intensities with peak values up to 500 Td and overall duration of about 10 ns. The 2D profiles of the streamer head electric fields were used as an experimentally obtained input for kinetic simulations of the streamer-induced air plasma chemistry. The radial and temporal computed distribution of the ground vibrational levels of the radiative states involved in the radiative transitions analyzed (337.1 nm and 391.5 nm), atomic oxygen, nitrogen, nitric oxide and ozone concentrations are vizualized and discussed in comparison with available models of the streamer phase of Blue Jet discharges in the stratosphere.