Numerical simulation of chemical reactions in PBS-like solution exposed to atmospheric-pressure plasmas*

Atmospheric-pressure plasma (APP) has been employed in various medical and biological research applications, including wound healing, bacteria sterilization, virus inactivation, and cancer treatment. In this study, zero-dimensional (0D, i.e., global) and one-dimensional (1D) numerical simulations were used to investigate chemical reactions, especially the generation and loss of reactive oxygen and nitrogen species (RONS) in a phosphate-buffered saline (PBS)-like solution (a pH buffer solution with NaCl) exposed to APPs [1,2]. First, we focused on the effects of charge-neutral reactive species generated in the gas-phase plasmas on the liquid-phase chemical reactions. It was found that hypochlorite ClO- generated in the solution consumed much of hydrogen peroxide H₂O₂ dissolved into the solution from the gas phase, which was in good agreement with an earlier experimental study [3]. Second, we examined the effects of injection of charged species of pulsed He plasmas into the PBS-like solution. The time-dependent injected fluxes of ions and electrons were evaluated with particle-in-cell/Monte Carlo (PIC/MCC) simulations of a pulsed He plasma at atmospheric pressure with a frequency of 10 kHz, an applied voltage of 1.5 kV, and a pulse duration of 15 nsec. It was found that, even if only charged species (e.g., He⁺, He₂⁺, and e^-) penetrated the PBS-like solution, chemically reactive species such as H₂O₂ and HOCl are generated in the solution (mostly in the reaction boundary layer, i.e., a thin solution layer at the gas-solution interface). The dynamics of liquid-phase chemical species due to the pulsed fluxes of gas-phase species from the plasma are also discussed.