Time-resolved measurements of NO2 concentration in pulsed discharges by high-sensitivity cavity ring-down spectroscopy

To describe the complex kinetics of formation and destruction mechanism of nitrogen dioxide (NO2),there is an increasing demand for real-time and in situ analysis of NO2 in the discharge region.Pulsed cavity ring-down spectroscopy (CRDS) provides an excellent diagnostic approach.In the present paper,CRDS has been applied in situ for time evolution measurement of NO2 concentration which is rarely investigated in gas discharges.In pulsed direct current discharge of NO2/Ar mixture at a pressure of 500Pa,a peak voltage of-1300V and a frequency of 30 Hz,for higher initial NO2 concentration (3.05 × 1014 cm-3,8.88 × 1013 cm-3),the NO2 concentration sharply decreases at the beginning of the discharge afterglow and then becomes almost constant,and the pace of decline increases with pulse duration;however,for lower initial NO2 concentration of 1.69 × 1013 cm-3,the NO2 concentration also decreases at the beginning of the discharge afterglow for 200 ns and 1 μs pulse durations,while it slightly increases and then declines for 2 μs pulse duration.Thus,the removal of low-level NO2 could not be promoted by a higher mean energy input.