Molecular admixtures and impurities in atmospheric pressure plasma jets

Abstract

A more complete understanding of reactive chemistry generated by atmospheric pressure plasma jets (APPJs) is critical to many emerging medical, agricultural, and water treatment applications. Adding molecular gases to the noble working gas which flows through the jet is a common method to tailor the resulting production of reactive oxygen and nitrogen species (RONS). In this paper, results are discussed from a computational investigation of the consequences of H 2 O and O 2 admixtures on the reactive chemistry of He APPJs flowing into humid air. This investigation, performed with a 2-dimensional plasma hydrodynamics model, addresses the RONS that are initially produced and the evolution of that chemistry on longer time scales. Without an admixture, the impurities in 99.999% pure helium are a major source of RONS. The addition of H 2 O decreases the production of reactive nitrogen species (RNS) and increases the production of reactive oxygen species (ROS). The addition of O 2 significantly decreases the production of RNS, as well as hydrogen-containing ROS, but increases the production of ROS without hydrogen. This selectivity comes from the lower ionization energy of O 2 compared to N 2 and H 2 O, which then allows for charge exchange reactions. These charge exchange reactions change the RONS which are produced in the afterglow by dissociative recombination. The consequences of impurities were also examined. Humid air impurities as low as 10 ppm in the helium can account for 79%-98% of the production of most RONS in the absence of an intentional admixture. The degree to which the impurities affect the RONS production depends on the electrode configuration and can be reduced by molecular admixtures.

Detecting trace methane levels with plasma optical emission spectroscopy and supervised machine learning

“…A change in intensity reflects an underlying change in the electron energy distribution which is responsible for excitation processes. A low concentration molecular admixture into a rare gas significantly changes the electron energy distribution by introducing additional inelastic low energy processes including the excitation of low lying (< 0.1 eV) vibrational and rotational states [23]. An increase in gas temperature is not uncommon with molecular admixtures [24].…”

Cold atmospheric plasma jet array for transdermal drug delivery

“…These results indicated that the TDD efficiency of the plasma jet array improved significantly when the 0.5% O 2 is mixed with the working gas, which is related to more ROS generated by the plasma, as reports indicated that the density of the ROS generated by the plasma increase when some oxygen is mixed into the working gas. [32][33][34][35] As the applied voltage increased to 9 kV 9 kHz, compared with 7 kV 7 kHz group, the TDD efficiency was not changed significantly after 3 min treatment, while 6 min treatment increased significantly, which shows that the plasma jet has a cumulative effect on enhancing TDD efficiency. The mixing of O 2 still plays an important role so that the efficiency of 6 min 7 kV 7 kHz He/O 2 mixture group is higher than 6 min 9 kV 9 kHz pure helium group.…”

Cold Plasma in Medicine and Healthcare: The New Frontier in Low Temperature Plasma Applications

“…For example the electric field can cause electroporation of cell membranes, allowing molecules (including ROS and RNS) to enter the cells and cause damage to the cell's internal organelles (including mitochondria) and macromolecules such as lipids, proteins, and DNA. To learn more about the physics and design of LTP sources the reader is referred to the following references [23,27,[54][55][56][57].…”