Recently, research found plasma-activated water (PAW) can process outstanding biological activities in agricultural and biomedical applications. 
PAW can be produced by various discharge structure below and above water surface. 
The commonly used discharge structures to make PAW include dielectric barrier discharge (DBD), plasma jet, glow discharge, spark discharge, corona discharge, and gliding arc discharge [1]. 
The reactive species generated in the gas phase plasma can transfer into the liquid and possibly form reactive species in the liquid or liquid–gas interface. 
Reactive oxygen species (ROS) and reactive nitrogen species (RNS) in PAW are considered the most important role of disinfection [2]. 
ROS mainly includes radicals, hydrogen peroxide, singlet oxygen, superoxide anions, and ozone, whereas RNS mainly includes nitrate, nitrite, peroxynitrite, nitric oxide radical, ammonia, and nitrogen [3]. 
The properties of PAW generated by different plasma methods are different. 
The higher plasma temperature is conducive to the gas-phase formation with higher nitrogen dioxide density, resulting in higher nitrate concentration [4, 5]. 
The PAW produced by spark discharge and microwave discharge mainly contains nitrogen-based chemicals such as nitrates and nitrites. 
In contrast, the PAW produced by glow discharge and DBD mostly contain hydrogen peroxide and nitrate.
PAW is usually acidic because of the reaction take place between the chemical species. 
It was stated that the proper combination of NTP and PAW generated a controlled pH (from 0 to 7) [6]. 
The acidification of water through the plasma reaction results in the generation of hydrogen peroxides, nitric acid, and peroxynitrous acid [7].
1.​Guo, D., et al., Plasma‐activated water production and its application in agriculture. 
Journal of the Science of Food and Agriculture, 2021.
2.​Liu, D., et al., Aqueous reactive species induced by a surface air discharge: Heterogeneous mass transfer and liquid chemistry pathways. 
Scientific reports, 2016. 6(1): p. 1-11.
3.​Thirumdas, R., et al., Plasma activated water (PAW): Chemistry, physico-chemical properties, applications in food and agriculture. 
Trends in Food Science & Technology, 2018. 77: p. 21-31.
4.​Vlad, I.-E. and S.D. Anghel, Time stability of water activated by different on-liquid atmospheric pressure plasmas. 
Journal of electrostatics, 2017. 87: p. 284-292.
5.​Niquet, R., et al., Characterising the impact of post‐treatment storage on chemistry and antimicrobial properties of plasma treated water derived from microwave and DBD sources. 
Plasma Processes and Polymers, 2018. 15(3): p. 1700127.
6.​Pemen, A., et al., Plasma activated water. 2016, WO Patent 2,016,096,751.
7.​Oehmigen, K., et al., The role of acidification for antimicrobial activity of atmospheric pressure plasma in liquids. 
Plasma processes and polymers, 2010. 7(3‐4): p. 250-257.