Two-dimensional simulations of an atmospheric-pressure streamer discharge at high gas temperatures were performed in humid air at initial gas temperatures, T 0 , in the range 300 K-600 K with the same electrode and applied voltage conditions as those used in Ono and Kamakura (2016 Plasma Sources Sci. Technol. 25 044007). The simulation was validated by comparing its results to experimentally obtained discharge currents, primary streamer velocities, and secondary streamer diameters and lengths. This paper discusses the mechanisms underlying the temperature effects in terms of the behaviour of the charged particles in the primary and secondary streamers. At T 0 =300 K, the main decay processes in the primary streamer are the electron recombination reactions with cluster ions and electron three-body electron attachment with O 2 and H 2 O, while the main decay process in the secondary streamer is the two-body electron attachment to O 2 . Although, at T 0 =600 K, the main decay processes in both streamers are still recombination and two-and three-body electron attachment reactions, the rates of these reactions decrease owing to the increase in the gas temperature, which leads to the increased conductivity of streamer discharge channels at high gas temperatures.

The axial distributions of the electron density in primary streamer discharge for atmosphericpressure air are simulated and compared with experimental data obtained by Inada et al (2017 J. Phys. D: Appl. Phys. 50 174005) using a highly temporally and spatially resolved measurement method for Shack-Hartmann-type laser wavefront sensors. The simulation is performed for the same electrode configuration, applied voltage, and gas component as the previously reported experiments. The simulation results show that the dissociative recombination reaction of electrons with cluster ion has an important influence on the axial distributions of the electron density during the primary streamer phase. However, the simulation results also indicate that the effect of the dissociative recombination reaction with cluster ion is limited to the primary streamer phase and the two-body attachment reaction of the electrons with O 2 is dominant for the decrease in electron density occurring during the secondary streamer phase. These findings contribute to improving the accuracy of the chemical reaction model of atmospheric-pressure streamer discharge, facilitating the development of atmospheric-pressure plasma applications.