In this work, we developed a portable device with low production and operation costs for generating ambient-air glow discharge (AAGD) that is transferred to the surface of flowing liquid and demonstrated its applicability to practical use in agriculture. An experiment procedure that ensured the stable treatment of various liquids was established. Additionally, it was found that humidity did not have a significant effect on the treatment process, which makes the use of the developed device possible in various locations. It was found that an _L-phenylalanine solution treated with AAGD allows simultaneous 40% hydroponic radish-sprout growth promotion with a bactericidal effect. Further, scalability and practical-application possibilities in hydroponic plant growth were discussed.

In this work, we developed a portable device with low production and operation costs for generating an ambient air low-current arc (AALCA) that is transferred to the surface of a treated liquid. It was possible to generate a stable discharge, irrespective of the conductivity of the treated liquid, as a sequence of corona, repeating spark, and low-current arc discharges. The estimated concentration of reactive oxygen and nitrogen species (RONS) in plasma-treated water (PTW) produced using AALCA treatment was two orders of magnitude higher than that of PTW produced using conventional He nonequilibrium atmospheric pressure plasma jets or dielectric barrier discharges. The strong bactericidal effect of the treatment using AALCA and the water treated using AALCA was confirmed by survival tests of Escherichia coli. Further, the possibility of treating a continuous flow of liquid using AALCA was demonstrated.

Ringer’s lactate solution was irradiated with non-equilibrium plasma under airtight conditions. The plasma-activated lactate (PAL) was produced with argon, oxygen, and nitrogen gases following purging of Ar. Cytotoxicity could be controlled by diluting PAL, and a killing effect was selectively obtained on cancer cells compared to normal cells for Ar+O₂+N₂ PALs. Nonetheless, cytotoxicity was partly reproduced by similar concentrations of H₂O₂ and NO₂ ⁻ in the PALs. The organics produced by plasma irradiation to lactate were investigated using nuclear magnetic resonance, and the generation of methyl amino species was confirmed.

For low-temperature atmospheric pressure plasma treatment applications, we developed a novel rotating arc jet operated using various gases, including ambient air. We demonstrate the operation of plasma via the injection of various gas mixtures and tune operation parameters to achieve a low-temperature gas output from the arc jet. The rotating arc jet has an efficiency two orders of magnitude higher in the generation of reactive oxygen and nitrogen species than commercially available conventional nonequilibrium atmospheric pressure plasma jets operated with He or Ar gases. The high concentration of reactive species and use of ambient air as a process gas is promising for biomedical and agriculture applications. This work is a step toward the commercial use of plasma jets operated with ambient air.