Inhibit ammonia volatilization from agriculture and livestock by air plasma-activated water

Ammonia volatilization in agriculture and livestock is a considerable cause of air pollution and a significant way of N loss. In this study, we propose a method of using air plasma-activated water (PAW) to inhibit ammonia volatilization from agriculture and livestock and report the inhibitory effect under different discharge times and concentration gradients. PAW was generated through needle–water discharge, while ammonia waters with different concentrations served as simplified models for ammonia release. The compositions of the gas/liquid products of the PAW and those after mixing with ammonia water were detected and analyzed. It was found that the PAW could effectively inhibit the NH₃ volatilization from ammonia water over a large range of conditions, however, NH₃ volatilization promotion could also happen in some cases. The inhibition rate (IR) generally increased with the longer discharge time of the PAW and decreased with the higher ammonia water concentration. As the discharge time increased, the PAW became more acidic and had more active N components, converting more volatile NH₃ to NH₄ ⁺ when mixed with ammonia water. Finally, a relationship model was developed between the IR and pH of the mixture. The IR basically decreased with the increase of the mixture pH, and reached ∼100% when a PAW with a discharge time of 7.5 min or 10 min was mixed with ammonia water with a mass fraction of 0.15%, or PAW of 10 min mixed with 0.25% ammonia water in this study, with the mixture pH lower than 8. The basic chemical process and possible reaction mechanisms were discussed. The proposed method not only effectively reduces ammonia volatilization but also adds more N elements in the form of NO₃ ⁻ and NH₄ ⁺, which further improves fertility.