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The nature and physical parameters of dielectric barrier discharges (DBDs) are determined by the presence of dielectric material in the discharge gap. The charging of the dielectric barrier is responsible for the non-thermal regime as it limits the local energy dissipation. In an operating DBD residual surface charges can influence the distribution and development of the plasma in the following discharge cycles1. In order to learn more about residual surface charge role an experiment with a rotating dielectric electrode and a pin electrode (325 μm tip radius) is realized2. The rotating dielectric barrier enables DBD-operation with DC high voltage and, the remaining surface charges are removed by a second grounded electrode which is sliding over the dielectric. Thus, single, repetitive microdischarges in air at atmospheric pressure are ignited without participation of residual surface charges. These microdischarges were investigated by ICCD camera, electrical measurements and time-correlated single photon counting (sub-ns, sub-mm and spectral resolution). For positive polarity of the pin electrode a positive streamer starting from the middle of the gap followed by a secondary wave starting from the metal electrode is observed. For negative polarity an anode directed wave of light and a weaker glow in front of the cathode are obtained.

A two-dimensional array of micro-discharges in air at atmospheric pressure is studied by cross correlation spectroscopy (CCS) [1]. The array consists of two insulated metal meshes and the discharge is generated by AC voltages at 20 kHz. A gas flow is applied through the array. The temporal resolution of CCS in the sub-ns range allowed to investigate the micro-discharges dynamics within a single micro-discharge hole end-on.

The inactivation of bacteria suspended in liquids by an atmospheric pressure plasma is a complicated and yet not well understood process, due to several constituents of the "plasma cocktail" in the plasma/gas phase which can contribute to bacteria inactivation and the transport and chemistry processes of the created species in the liquid phase. To investigate the main players in the bacteria inactivation processes we use a RF atmospheric pressure plasma jet which is used for remote bacteria treatment. The plasma jet is constructed to allow accurate power measurements. Mass spectrometry, optical emission spectroscopy as well as electrical diagnostics have been used to investigate the amount of charged and reactive species and UV-emission reaching the water surface. We show that with the chosen treatment conditions, reactive species (ROS and RNS) concentrations and probably (V)UV emission are high enough to induce chemistry in the liquid phase leading to bacteria inactivation, while the electric field and charged particles are too low to induce observed effects. To further determine the role of the reactive species interaction within the liquid, nitrite, nitrate and hydrogen peroxide concentrations have been obtained by ion chromatography and colorimetric methods. Combined with measured and estimated values of the reactive species in the gas phase we use a 0D-solution kinetics model to calculate other species expected in the liquid phase and important for bacteria inactivation, which have not been measured. We show that the obtained concentrations of HNO2, ONOO and H2O2 are in the same range as reported values in literature of the minimum inhibitory and bactericidal concentrations.

Summary form only given. The application of atmospheric pressure discharges in new fields like environmental protection, surface treatment or life-sciences requires a profound knowledge on the plasma parameters and properties. This includes (1) the characterization of the breakdown processes triggering plasma chemistry, (2) the proper determination of the electrical parameters and (3) the description of the dominant chemical pathways. The contribution aims to present new approaches regarding these three topics for pulsed driven Dielectric Barrier Discharges in particular. It will be shown by fast electrical, optical and spectroscopic methods that the ignition, breakdown statistics and spatio-temporally resolved development of pulsed DBD microdischarges is controlled by the properties of the power supply (duty cycle, frequency, amplitude varied) as well as the composition of the gas1. In particular the starting point of the microdischarge ignition can be changed which is a new effect in DBDs caused by electric field rearrangement in the gap due to positive ion development. Surface processes at the dielectric barriers influencing this behavior will be discussed, too. The determination of electrical parameters such as discharge current, gas gap voltage, instantaneous power and energy as well as the charge transferred through the gas gap based on a simple equivalent circuit will be presented. The proposed approach accurately accounts the displacement current and key capacitance values, which inexactly determination are a source of experimental errors in particular in case of pulsed driven DBDs. The presented approach is consistent with sinusoidal-voltage driven or miniature pulsed driven DBDs. We believe that these new insights on electrical characterization are an important input for those who are working with DBDs, since the electrical parameters are mandatory information. The characterization of the dominant chemical pathways of advanced plasma processes is usually focused on the volume processes only. This contribution will discuss several examples which shall emphasize, that secondary effects must be considered, too. These shall cover the topics of adsorption-enhanced VOC conversion by DBD plasma treatment, NOx conversion and indirect plasma treatment of liquids for antimicrobial and chemical decontamination.

The application of atmospheric pressure discharges in new fields like environmental protection, surface treatment or life-sciences requires a profound knowledge on the plasma parameters and properties. This includes the characterization of the breakdown processes triggering plasma chemistry, the proper determination of the electrical parameters and the description of the dominant chemical pathways. This contribution aims to present new approaches regarding these three topics for pulsed driven Dielectric Barrier Discharges (DBDs) in particular. Fast electrical, optical and spectroscopic methods enable the study of ignition, breakdown statistics and spatio-temporally resolved development of pulsed DBD microdischarges. The determination of electrical parameters such as discharge current, gas gap voltage, instantaneous power and energy as well as the charge transferred through the gas gap is based on a simple equivalent circuit which is consistent with sinusoidal-voltage driven or miniature pulsed driven DBDs. The characterization of the dominant chemical pathways of advanced plasma processes discusses also several examples including secondary effects, such as adsorption-enhanced VOC conversion by DBD plasma treatment.

Summary form only given. The treatment of liquid with a surface dielectric barrier discharge (DBD) under atmospheric pressure in air results in pH decrease and generation of nitrate (NO 3 −), nitrite (NO 2 −) and hydrogen peroxide (H 2 O 2 ) in water. Even, after plasma treatment antimicrobial effects on suspended microorganisms were investigated [1] [2].

Summary form only given. There is an increasing interest in atmospheric pressure discharges for technological applications. Due to their low gas temperature, high electron energy and the presence of active species these discharges have a high potential for plasma chemistry e.g. for ozone production as well as gas and water purification1. Besides corona discharges and micro hollow cathode discharges, dielectric barrier discharges are often used in this field of application. Here, sinusoidal driven ones are basically used in practice. In last years however, there are applications where pulsed driven discharges show a better efficiency in plasma-chemical application (e.g. ozone generation2) than sinusoidal driven ones. This finding forces systematic studies in this matter.

DBD plasma treatment of non-buffered water based liquids under atmospheric conditions resulted in microorganism inactivation accompanied by acidification as well as generation of nitrite, nitrate, and hydrogen peroxide1. In an additional study, microorganisms were incubated with sodium chloride solution immediately as well as 30 min after DBD plasma treatment of the liquid. An effective inactivation was found under these conditions, too. These results led to the conclusion that microorganism inactivation was caused mainly by stable reactive species generated in the liquid as a result of plasma treatment. More detailed investigations using variable liquid volumes and surfaces demonstrated that acidification as well as generation of nitrite, nitrate, and hydrogen peroxide proceeds at the gas-liquid interface. A subsequent distribution in the bulk liquid seems to be caused both by diffusion and convection processes. However, addition of nitrite, nitrate, hydrogen peroxide or acid alone or as mixtures to microorganism suspensions did not cause any biological effects. Using additional results of liquid treatment by atmospheric pressure plasma in an argon enriched atmosphere instead of air, possible mechanisms as well as stable reactive species being responsible for biological effects like microorganism inactivation are discussed.