NH 3 impact on plasma-activated water: physics and chemistry insights

Abstract This letter delves into the impact of varying ammonia (NH 3 ) from 0% to 100% in the feed gas on the physics and chemistry characteristics of plasma-activated water (PAW) prepared by air surface discharge plasma treatment. Results demonstrate that increasing NH 3 concentration significantly alters discharge modes, reactive species generation, and PAW composition. The mode transition changes from a distinct filamentary discharge in pure air to a weaker, more diffuse-like discharge in NH 3 -rich mixtures, highlights the strong influence of gas composition of plasma. This transition is accompanied by a marked reduction of excited nitrogen species, showing a shift from nitrogen oxide-dominated chemistry to the formation of ammonium nitrate (NH 4 NO 3 ). Notably, higher levels of NH 3 would promote NH 4 NO 3 formation while inhibiting the generation of key species such as H 2 O 2 , NO 2 − , and ONOO − . Our findings demonstrate that NH 3 concentration is a key parameter for tailoring PAW, enabling controlled synthesis from nitrogen oxides to NH 4 NO 3 to meet specific application needs.