Discharge characteristics and reactive species production of unipolar and bipolar nanosecond pulsed gas–liquid discharge generated in atmospheric N₂

In this paper, unipolar pulse (including positive pulse and negative pulse) and bipolar pulse voltage are employed to generate diffuse gas–liquid discharge in atmospheric N₂ with a trumpet-shaped quartz tube. The current–voltage waveforms, optical emission spectra of excited state active species, FTIR spectra of exhaust gas components, plasma gas temperature, and aqueous H₂O₂, \rmNO_2^-, and \rmNO_3^- production are compared in three pulse modes, meanwhile, the effects of pulse peak voltage and gas flow rate on the production of reactive species are studied. The results show that two obvious discharges occur in each voltage pulse in unipolar pulse driven discharge, differently, in bipolar pulse driven discharge, only one main discharge appears in a single voltage pulse time. The intensities of active species (OH(A), and O(3p)) in all three pulsed discharge increase with the rise of pulse peak voltage and have the highest value at 200 ml min⁻¹ of gas flow rate. The absorbance intensities of NO₂ and N₂O increase with the increase of pulse peak voltage and decrease with the increase of gas flow rate. Under the same discharge conditions, the bipolar pulse driven discharge shows lower breakdown voltage, and higher intensities of excited species (N₂(C), OH(A), and O(3p)), nitrogen oxides (NO₂, NO, and N₂O), and higher production of aqueous H₂O₂, \rmNO_2^-, and \rmNO_3^- compared with both unipolar positive and negative discharges.