It is demonstrated that direct exposure of deionized water to a dielectric barrier discharge (DBD) plasma creates an acid (pH % 2) and is in fact, a strong oxidizer (providing, e.g., peroxidation of a cell membrane). This study addresses the question: which acid is created in water by plasma treatment. Two major possibilities are considered: nitric/nitrous acid and an acid which consist of a hydrogen cation (H þ ) and a superoxide anion (O À 2 ), which, for the lack of a better term, we call plasma acid. The presence of nitric/nitrous acid in the water after plasma treatment in air is confirmed, although the observed pH % 2 cannot be completely explained by the production of nitric acid. Moreover, experiments with oxygen-plasma treatment of water also lead to high acidity, without production of nitrogen based acids at all. Therefore, O À 2 , the conjugate base of the plasma acid, is at least partially responsible for both lowering of the pH and the increase in the oxidizing power of the solution. Experiments indicate that peroxides such as H 2 O 2 and O À 2 , together with an acidic environment are likely to be responsible for the oxidation properties of the plasma treated water. This plasma acid remains stable for at least a day, depending on the gas where plasma is generated, but the effect is temporal. Existence of a temporal and stable oxidizer created using the plasma treatment of pure water not only raises interesting scientific questions and possibilities, but is also likely to provide many applications in situations where direct plasma treatment may be difficult to achieve. Plasma Process. Polym. 2012,

Cold atmospheric pressure plasmas have emerged as a promising new tool for medical applications. Compared to conventional thermal plasma, such as arc coagulators and desiccators, cold plasma can be more selective in its application and may be used for effective sterilization of skin and wound tissue, wound healing and tissue regeneration, cancer treatment and blood coagulation. One of the key questions that has to be answered before these plasma technologies are introduced in medical practice is the safety of plasma treatment of living tissues, i.e. toxic dose levels of plasma exposure should be determined. It is well established that porcine (pig) skin closely resembles human skin; hence we evaluated the potential toxic effects of plasma treatment on intact and wounded skin in a Yorkshire pig model. Varying doses of Floating Electrode Dielectric Barrier Discharge (FE-DBD) and microsecond Pin-to-Hole Spark Discharge (PHD) plasmas were applied to determine a dosage regime where tissue damage occurs.

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Non-thermal atmospheric pressure plasma applied to the surface of water can oxidize organic molecules in the solution and kill bacteria in it. Ozonation of water produce a solution that retains its oxidation potential for several minutes. We show that direct exposure of deionized water not only to ozone but to other neutral and charged species produced in plasma creates a strong oxidizer in this water which, for the lack of a better term, we can call plasma acid.Plasma acid can remain stable for much longer time than ozonated water and its oxidizing power may be linked to the significant lowering of its pH. We report experiments that demonstrate plasma acid's stability. We also show that observed pH of as low as 2.0 cannot be completely accounted for by the production of nitric acid; and that the conjugate base derived from superoxide is at least partly responsible for both, lowering of the pH and increase in the oxidizing power of the solution. Existence of a stable oxidizer created using plasma treatment of pure water not only raises interesting scientific questions and possibilities, but is likely to find many applications in situations where "on the spot" plasma treatment may be difficult to achieve.

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