Investigation Of O₃ And NO₃ In Atmospheric Pressure Surface Discharge By Optical Absorption Spectroscopy

Plasma medicine is an emerging interdisciplinary field that integrates plasma and clinical medicine.The in-situ quantitative diagnosis of reactive oxygen species and reactive nitrogen species?RONS?in the gas phase is a key issue in plasma medicine.The processes of generation and efficient delivery of reactive oxygen species and reactive nitrogen species in the low temperature plasma are similar to natural cells.Due to the advantage of generating a large-area plasma close to room temperature and independent of the electrical characteristics of the sample to be processed in the afterglow region,surface discharge has attracted widespread attention in the field of plasma medicine.The quantitative analysis and the temporal evolution of RONS produced by plasma sources is an important prerequisite for systematic study of the interaction between RONS generated by plasma and cells and tissues.From a deeper perspective,this correlation can be considered as one of the keys to the research of suitable plasma sources and effective treatment methods.The main research contents of this thesis including:An atmospheric pressure surface discharge generator has been designed and built.The discharge electrodes adopted the structure that composed of a copper grid ground electrode,a high-voltage planar electrode and a dielectric plate sandwiched there between,and pulse modulation was performed on the continuous AC sinusoidal high-voltage power supply.The discharge characteristics of atmospheric pressure surface discharge and the dependence between discharge power density and applied voltage were studied.An optical absorption spectral system has been established for measuring RONS species in the plasma.The balanced deuterium-halogen lamp with stable intensity is selected as the light source.With photomultiplier tube,monochromator and oscilloscope,the concentrations of O3 and NO3 in the afterglow region of the plasma were detected.The temporal evolution of ozone concentration at the different flow rates of helium/synthetic air was measured for studying the influence of helium on ozone concentration.The discharge time range was 0 to 120 s,with voltage 4.5 kV,the modulation frequency 50 Hz,and the duty cycle ratio 66.7%.It was observed that as the flow rate of helium increased,the ozone concentration gradually increased during the 120 s discharge time.The trend of average ozone concentration with power density within 10-15 s after the start of discharge was characterized,and the overall influence of power density on ozone concentration was measured.The temporal evolution of the concentrations of O3 and NO3 in the plasma afterglow region were investigated varying the electrical power density applied to the plasma source by absorption spectroscopy.The quenching phenomenon of O3 and NO3 was observed and the mechanism for the generation and quenching of O3 and NO3 was discussed and analyzed.The quenching phenomenon of O3 was mainly related to the change of NO concentration,and the time evolution of NO3 and O3 concentration was strongly correlated.By the way,water vapor also had a certain influence on the change of O₃ and NO₃ concentration.