In this study, a dielectric barrier discharge device with needle-plate electrodes was used to investigate the characteristics of the micro-discharge in argon at one atmospheric pressure by an optical method. The results show that there are two discharge modes in the dielectric barrier discharge, namely corona mode and filamentary mode. The corona discharge only occurs in the vicinity of the needle tip when the applied voltage is very low. However, the filamentary discharge mode can occur, and micro-discharge bridges the two electrodes when the applied voltage reaches a certain value. The extended area of micro-discharge on the dielectric plate becomes larger with the increase in applied voltage or decrease in gas pressure. The variance of the light emission waveforms is studied as a function of the applied voltage. Results show that very narrow discharge pulse only appears at the negative half cycle of the applied voltage in the corona discharge mode. However, broad hump （about several microseconds） can be discerned at both the negative half cycle and the positive half cycle for a high voltage in the filamentary mode. Furthermore, the inception voltage decreases and the width of the discharge hump increases with the increase in applied voltage. These experimental phenomena can be explained qualitatively by analyzing the discharge mechanism.
A zero-dimensional model which includes 56 species of reactants and 427 reactions is used to study the behavior of charged particles in atmospheric plasmas with different ionization degrees at low altitude （near 0 km）. The constant coefficient nonlinear equations are solved by using the Quasi-steady-state approximation method. The electron lifetimes are obtained for afterglow plasma with different initial values, and the temporal evolutions of the main charged species are presented, which are dominant in reaction processes. The results show that the electron number density decays quickly. The lifetimes of electrons are shortened by about two orders with increasing ionization degree. Electrons then attach to neutral particles and produce negative ions. When the initial electron densities are in the range of 10l~ ~ 1014 cm-3, the negative ions have sufficiently high densities and long lifetimes for air purification, disinfection and sterilization. Electrons, O（2,-）, O（4,-） CO（4,-） and CO（3,-） are the dominant negative species when the initial electron density neo ≤ 1013 cm^（-3）, and only electrons and CO3 are left when neo 〉 1015 cm^（-3）. N（＋,2）, N＋ and O（＋,2） are dominant in the positive charges for any ionization degree. Other positive species, such as 0（＋,4）, N（＋,3）, NO（＋,2）, NO（＋,2）, Ar（＋,2） and H3O＋. H2O, are dominant only for a certain ionization degree and in a certain period.
