Different gases added to cold atmospheric plasmas can lead to the production of reactive species, such as reactive oxygen species (ROS) and reactive nitrogen species (RNS). Because ROS and RNS can be crucial in plasma applications, Liu et al. developed a model to better understand how they are generated.
“Helium plasma is widely used for biomedical applications, in which air gas impurities inevitably exist or are even artificially added into helium to facilitate the production of ROS and RNS,” said author Dingxin Liu.
The authors aimed to quantify how many ROS and RNS could be produced with varying amounts of air gas impurities. Regardless of air concentration, they found atomic oxygen to be the dominant ROS and nitrogen oxide to be the dominant RNS, though the reactive species density varies. Additionally, they determined the main production pathways for both ROS and RNS.
“What surprised me the most was that the chemical pathways of ROS are almost separated from that of the RNS, and the main chain connecting the two chemical networks is very simple,” said Liu, referring to the oxidation of atomic nitrogen to form nitrogen oxide from hydroxyl.
To complement the simulation, the authors used an experimental setup where they measured the emission spectra of helium plasma driven by a sinusoidal voltage. However, they note additional experiments are necessary in order to fully characterize the reactions.
“Much remains unknown about the plasma chemistry in helium with air gas impurities, and therefore, a lot of work needs to be done in the future,” Liu said. “Our work is at an early stage, and most importantly, the simulation results need to be further validated by experiments.”
Source: “1D fluid model of RF-excited cold atmospheric plasmas in helium with air gas impurities,” by Yifan Liu, Dingxin Liu, Jishen Zhang, Bowen Sun, Aijun Yang, and Michael G. Kong, Physics of Plasmas (2020). The article can be accessed at https://doi.org/10.1063/1.5145033.
