Cold atmospheric-pressure plasma jet generates rich reactive species including reactive oxygen species and reactive nitrogen species with gas temperature close to or at room temperature, which is very attractive for applications such as plasma medicine. However, under one atmospheric pressure, due to the high electron–neutral particles collision frequency (10^11–12/s), it is difficult to generate atmospheric pressure plasma while keeping the gas temperature close to or at room temperature. Furthermore, when air rather than noble gases is used as working gas, due to the low energy levels of rotational and vibrational states of nitrogen and oxygen, it becomes extremely challenging to generate cold atmospheric pressure air plasma jet (CAAP-J) with gas temperature close to or at room temperature. Fortunately, after decades of research, several CAAP-Js have been reported. In this review, the state-of-the-art of the development of CAAP-Js is presented. The CAAP-Js are grouped into six categories based on their electrode configuration. A brief discussion on each group of the CAAP-Js is presented. Moreover, the physics of CAAP-Js is discussed, including the dynamics, the striation phenomenon, the temporal behavior of plasma parameters, and the nonequilibrium characteristic of CAAP-Js. Furthermore, the measurements of the reactive species generated by CAAP-Js are briefly reviewed. Finally, discussions and perspective of future research on CAAP-Js are presented.

In this study, the propagation mechanism of plasma jet and some bio‐medical applications are investigated by two‐dimensional numerical model. The key equations of plasma physics and chemistry related with plasma jet are firstly introduced. The simulation results suggest that the sheath forms near the dielectric tube inner surface, which results in the plasma channel to shrink in the radial direction inside the dielectric tube. The photoionisation of air species plays a crucial role in the transition from the localised discharge to streamer. The Penning ionisation increases the electric conductivity of the plasma channel and facilitates the formation of ring‐shaped plasma bullet. For the plasma jet in the open air, electron‐impact dissociation of H ₂ O, electron neutralisation of H ₂ O ⁺ , as well as dissociation of H ₂ O by O(1D) are found to be the main reactions to produce OH. For micro plasma jet, the higher ignition voltage as the tube diameter decreased is attributed to the deceasing pre‐avalanche electron density inside the tube. The simulation of plasma treatment of bacteria biofilm indicates that the mean free path of charged species in µm scale permitted the plasma penetrate into the cavity of the biofilm, and the structure of the biofilm results in the non‐uniform distribution of ROS and RNS. The simulation of plasma treatment of cells immersed in liquid suggests that the HO ₂ generated by plasma aqueous species is the only way for superoxide to penetrate cell membrane and damage cytosolic fumarase B.