Afterglow chemistry of atmospheric-pressure helium–oxygen plasmas with humid air impurity

Abstract

The formation of reactive species in the afterglow of a radio-frequency-driven atmospheric-pressure plasma in a fixed helium-oxygen feed gas mixture (He+0.5%O 2 ) with humid air impurity (a few hundred ppm) is investigated by means of an extensive global plasma chemical kinetics model. As an original objective, we explore the effects of humid air impurity on the biologically relevant reactive species in an oxygen-dependent system. After a few milliseconds in the afterglow environment, the densities of atomic oxygen (O) decreases from 10 15 to 10 13 cm −3 and singlet delta molecular oxygen (O 2 ( 1 D)) of the order of 10 15 cm −3 decreases by a factor of two, while the ozone (O 3 ) density increases from 10 14 to 10 15 cm −3 . Electrons and oxygen ionic species, initially of the order of 10 11 cm −3 , recombine much faster on the time scale of some microseconds. The formation of atomic hydrogen (H), hydroxyl radical (OH), hydroperoxyl (HO 2 ), hydrogen peroxide (H 2 O 2 ), nitric oxide (NO) and nitric acid (HNO 3 ) resulting from the humid air impurity as well as the influence on the afterglow chemistry is clarified with particular emphasis on the formation of dominant reactive oxygen species (ROS). The model suggests that the reactive species predominantly formed in the afterglow are major ROS O 2 ( 1 D) and O 3 (of the order of 10 15 cm −3 ) and rather minor hydrogen-and nitrogen-based reactive species OH, H 2 O 2 , HNO 3 and NO 2 /NO 3 , of which densities are comparable to the O-atom density (of the order of 10 13 cm −3 ). Furthermore, the model quantitatively reproduces the experimental results of independent O and O 3 density measurements.

Effect of Additive Oxygen on the Reactive Species Profile and Microbicidal Property of a Helium Atmospheric Pressure Plasma Jet

“…These were estimated based on ref . by scaling down the oxygen‐based species’ densities by the factor of 100.…”

“…This experimental work is complemented by a two‐dimensional (2D) numerical model of the gas dynamics and the afterglow chemistry in the APPJ. The reaction scheme and the initial conditions for the model were based on previous work on the characterization of He‐APPJs . The model itself was employed in order to understand several interesting phenomena that were observed and are a consequence of the interplay of gas dynamics and the chemistry in the jet.…”

Interactions of a Non‐Thermal Atmospheric Pressure Plasma Effluent with PC‐3 Prostate Cancer Cells

“…The plasma produced species in this source have been investigated through numerical simulations and experiments both in the plasma core and in the effluent emanating from it . The plasma source is a very efficient source for reactive oxygen and nitrogen species (RONS) including atomic oxygen (O), atomic nitrogen (N), ozone (O 3 ), singlet delta oxygen (O 2 (1D)), hydroxyl radicals (OH), and nitric oxide (NO) . These species have been previously, even individually, implicated as important in many biological systems and therapeutic applications .…”

“…Relatively recently non‐thermal plasmas produced at atmospheric pressure have shown great potential for having a similar impact in biomedicine . They offer a unique chemically reactive environment, producing high densities of a range of different reactive species very efficiently . Furthermore, their properties can be changed in order to tailor their chemical composition for the particular application required …”

Controlled production of atomic oxygen and nitrogen in a pulsed radio-frequency atmospheric-pressure plasma

“…Atomic oxygen and nitrogen have been shown to play key roles in the chemical kinetics of these systems [26][27][28][29][30][31]. In this study, we have therefore combined the use of rf pulse modulation with an air-like admixture (0.1% N 2 /O 2 at 4:1) to a helium-fed APPJ to more closely match the conditions of prospective applications.…”