A device for obtaining and applying a disinfectant agent and method of use are provided. The device includes a pre-processing cascade unit that activates (ionizes) air, with the activated air being supplied by an air pump to an inlet of a sprayer, where the activated air mixes with an initial working fluid (distilled water) to form an activated air-working fluid aerosol mixture that is sprayed by the sprayer into a reactor of cone-shaped volumetric cold plasma that includes divergent discharge electrodes. The device further includes a unit for generating high-voltage pulses of a nanosecond duration that is connected to the discharge electrodes and that causes the electrodes to generate electrical discharges. Upon the mixture coming into contact with the electrical discharges, potent disinfectant agents (such as peroxynitrite and one or more peroxynitrite's precursors or derivatives) are synthesized and expelled from the device.