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 500 Pa, 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.