Reduced Kinetic Modelling of Reactive Oxygen and Nitrogen Species Formation in Microwave Plasma Jets

Cold atmospheric-pressure microwave plasma jets are crucial sources of reactive oxygen and nitrogen species (RONS) in the fields of biomedicine, environment, and industry. A reduced kinetic model has been constructed to model RONS production in microwave-driven plasma jets at different process parameters in this paper. The model employs a simplified system of coupled ordinary differential equations representative of the dominant plasma-chemical reactions to characterize the time evolution of six high-interest species (OH, O, O3, NO, NO2, and H2O2). The influence of gas composition, gas flow rate, surface humidity, and microwave power on RONS generation was studied. The results demonstrated that oxygen concentration promotes the formation of atomic oxygen and ozone, and the air mixture concentration favors the generation of nitrogen oxides. Higher humidity conditions promoted hydroxyl-based chemistry and H2O2 formation, and stronger microwave power resulted in higher number densities of all the species being studied. The results also showed that the RONS production is determined by the competition between precursor supply and residence time, which results in maximal reactive-species production at intermediate gas-flow rates. Under most operating conditions, the highest predicted number densities were for ozone. Model predictions were consistent with experimentally reported trends for atmospheric-pressure microwave plasma jets. Quantitative validation against experimentally reported densities of OH, O, O3, NO, and NO2 yielded an average relative deviation of approximately 7.4%. Sensitivity analysis identified the effective dissociation processes of O2 and H2O, together with microwave power, as the dominant parameters controlling model predictions. The proposed model provides a computationally efficient framework for analyzing and optimizing RONS generation in microwave plasma jet systems.