ORIGINAL PAPER The Role of Interfacial Reactions in Determining Plasma–Liquid Chemistry Carly E. Anderson 1 • Nico R. Cha 1 • Alexander D. Lindsay 2 • Douglas S. Clark 1 • David B. Graves 1 Received: 24 May 2016 / Accepted: 9 August 2016 / Published online: 23 August 2016 Ó Springer Science+Business Media New York 2016 Abstract In this work, we investigate the production of highly oxidative species in solutions exposed to a self-pulsed corona discharge in air. We examine how the properties of the target solution (pH, conductivity) and the discharge power affect the discharge stability and the production of H 2 O 2 . Indigo carmine, a common organic dye, is used as an indicator of oxidative strength and in particular, hydroxyl radical (OH  ) production. The observed rate of indigo oxidation in contact with the discharge far exceeds that predicted from reactions based on concentrations of species measured in the bulk solution. The generation of H 2 O 2 and the oxidation of indigo carmine indicate a high concentration of highly oxidizing species such as OH  at the plasma–liquid interface. These results indicate that reactions at the air plasma–liquid interface play a dominant role in species oxidation during direct non-equilibrium atmospheric pressure plasma treatment. Keywords Plasma activated water (PAW)  Reactive oxygen species  Corona discharge  Indigo carmine  Non-equilibrium atmospheric pressure plasma (NEAPP) Introduction Devices to produce ‘‘cold’’ (non-equilibrium) atmospheric-pressure plasma (NEAPP) are gaining increasing attention for a wide range of applications. In addition to promising work in the field of plasma medicine [1–4], NEAPP has also been shown to effectively decontaminate food [5] and surfaces [6, 7], degrade organic pollutants [8–10], and open Electronic supplementary material The online version of this article (doi:10.1007/s11090-016-9742-1) contains supplementary material, which is available to authorized users. & David B. Graves graves@berkeley.edu 1 Department of Chemical and Biomolecular Engineering, University of California, Berkeley, CA, USA 2 Department of Nuclear Engineering, North Carolina State University, Raleigh, NC, USA 123 Plasma Chem Plasma Process (2016) 36:1393–1415 DOI 10.1007/s11090-016-9742-1