Arc discharge with argon and nitrogen was generated across the long electrode gap distance of 400 mm to produce a stable thermal plasma and large volume with low power under atmospheric pressure. In the case of nitrogen as plasma forming gas, an increase of the gas flow rate increases the arc voltage, thus the center temperature of the arc column reached higher. For the argon arc, the arc voltage decreases with increasing gas flow rates. Due to the arc constriction in both cases of nitrogen and argon, the center temperature of the arc column increases under the constant current. The result of emission intensity distribution across nitrogen arc column reveals that the arc column diameter increases with increasing gas flow rate because of the increase of the input power. On the other hand, in the argon arc, the diameter decreases by strong thermal pinch in large flow rate of argon. The measured excitation temperature is uniform along with axial direction of the arc column which is an important feature for waste materials processing due to the long direct current arc plasma that provides long residence time for injected materials. (C) 2012 Elsevier B. V. All rights reserved.