The effect of the gap distance between an atmospheric-pressure plasma jet nozzle and liquid surface on OH and N2 species concentrations

An argon plasma jet at atmospheric pressure was operated at various gap distances between the nozzle of the plasma jet and the water surface in order to study the formation of OH and N2 species in the vicinity of the water surface. Plasma was generated using a 24 kHz sinusoidal power supply at a steady gas flow-rate of 200 sccm. The electron temperature and rotational temperature of gas species were measured using optical emission spectroscopy and found to decrease with increasing gap distance. Meanwhile, the electron density calculated from jet current measurement increased with increasing gap distance. The average OH concentration reduced from 6.10 × 1015 cm−3 to 1.35 × 1015 cm−3, as the gap distance increased from 1 to 4 mm. The 337 nm N2 second positive system studied by optical emission spectroscopy and temporal emission signals increased with increasing gap distance. Plasma activated water was also made from various gap distances in order to confirm the presence of particular reactive oxygen or nitr...