Non-thermal microplasma jets generated under atmospheric pressure by means of radio-frequency of 13.56 MHz and low-frequency of several tens of kilohertz are characterized. They show several distinct discharge characteristics. Two operation modes of the plasma are observed when the single pin electrode is utilized and separated by the remote ground, and where plasma is sustained between the pin electrode and the ground ring electrode. The electrical characteristic of discharges and various effects of the ground ring electrode are presented. We observe that the emission spectra are dominated by the presence of excited nitrogen, helium, and nitrogen ions. Highly reactive radicals such as hydroxyl (OH) and atomic oxygen are also detected. With the addition of a ground ring electrode, the discharge current and optical emission intensities from the plasma plume are enhanced significantly indicating that the generated plasma is near the glow discharge mode. (C) 2009 Elsevier B.V. All rights reserved.