AbstractNonthermal plasma (NTP) is a promising technology for the removal of persistent organic contaminants in wastewater thanks to its ability to generate powerful oxidizing species. In this work, a gliding arc discharge NTP was used for an experimental study to investigate the influence of relative humidity (RH) on reactive species generation depending on a plasma atmosphere (air and oxygen). In addition, an organic dye, Eriochrome Black T (EBT), was treated to investigate the removal potential of this plasma. Dimethyl sulfoxide was used as chemical probe for the detection of OH• and as a radical scavenger to explore the role of OH• in EBT removal. Hydrogen peroxide, nitrite, and nitrate quantification was also assessed. Results indicated that for air plasma, a RH of 30% contributed to the highest oxygen species generation, while dry conditions gave the best results under O2 plasma. The treatment of EBT revealed that humid air plasma (RH=30%) is more effective regarding decolorization. However, mineralization experiments showed that O2 plasma is more capable of mineralizing an EBT solution. The use of a radical scavenger showcased the potential of plasma gliding arc in humid air for the removal of organic contaminants when radicals’ reactivity is inhibited. Therefore, this study may provide an effective and feasible method of applying NTP in wastewater treatment.