Diagnostics of chemical composition of ``plasma acid'' generated in water using oxygen DBD plasma

Plasma treated water has been studied recently by many groups due to its typically high oxidative properties that are interesting for a number applications, including biomedicine and agriculture. In the case of air-plasma treatments, water becomes acidic due to generation of nitric and nitrous acids, while oxidative properties are due to ROS and RNS, including \textbullet OH, \textbullet O, H2O2, NO3-, ONOO-. Here, we report on identification of acidity source of oxygen DBD treated water, sometimes referred as ``plasma acid'', with strong but temporary oxidizing properties. The conjugate base of this oxygen plasma-produced acid remained unidentified. The results presented here suggest that ``plasma acid'' contains unstable O2- and O3- as possible anion species.