Reactive species in surface micro-discharge in air and their influencing factors

The reactive species in cold atmospheric-pressure plasmas play a key role in various application fields, such as biomedicine, environmental protection, nanotechnology, etc. In order to further investigate the composition and the number density of the reactive species and their influence conditions, a 0-D global model is developed for surface micro-discharge in atmospheric-pressure air, which incorporates 54 species and 624 chemical reactions. The reactive species and their production mechanism in the plasma and the downstream air region are then studied. It is found that the main species in the downstream air region are O₃, N₂O₅, N₂O, HNO₃, NO₃, H₂O₂, HNO₂, and NO₂. The number densities of reactive species increase linearly with the input power density from 250 W/m² to 1000 W/m², but the energy efficiency for the production of reaction species decreases. The number densities of reactive species decrease to some extent when the air region thickness increases from 1 mm to 10 mm, but the energy efficiency increases sharply. As the gas temperature increases from 300 K to 320 K, the number densities of reactive oxygen species decrease, on the contrary, the number densities of reactive nitrogen species increase. The number densities and production efficiency of reactive species are strongly dependent on the discharge conditions like the input power, the air region thickness, and the gas temperature.