Optical Emission Spectroscopy of Lightning Impulse Discharges in Long Air Gaps with and without Water Mist

This work aims to study the various parameters of LI (lightning impulse) discharge channels in an air gap, i.e., the reactive radicals, electron density and channel temperature, and the influence of water mist on the reactive radicals, electron density and channel temperature of the discharge using optical emission spectroscopy. During a LI discharge in air, the gas in the air becomes highly ionized, and the spectra of which are similar to reference spectra of natural lightning. The electron density and channel temperature of the discharges in air under a LI voltage is ca. 3×10 ²³ m ^-3 and ca. 13,000 K, respectively, both of which are lower than those of natural lightning. Compared with LI discharges in air, more OH and OH ⁺ radicals are detected when the discharge takes place in a water mist-air mixture, indicating the partial decomposition of water molecules on the surface of water droplets during the LI discharge. The addition of water mist results in an 8.8-10.7% lower electron density than during LI discharges in air. However, the addition of water mist does not obviously influence the channel temperature of the air discharge.