High-Sensitivity In-Situ Diagnosis of NO 2 Production and Removal in DBD Using Cavity Ring-Down Spectroscopy

A highly-sensitive in-situ diagnosis approach for nitrogen dioxide (NO ₂ ) has been developed in dielectric barrier discharge (DBD) based on pulsed cavity ring-down spectroscopy (CRDS). Absorption bands of NO ₂ in a spectral region from 508 nm to 509 nm were used, and a detection limit of 17.5 ppb was achieved. At this level of sensitivity, the quantitative and real-time monitoring of the production and removal of NO ₂ are accomplished for the first time in the discharge region. By measuring the removal amount and rate at different NO ₂ initial number densities from 1.54 × 10 ¹³ cm ⁻³ to 2.79 × 10 ¹⁴ cm ⁻³, we determined the relationship between them and NO ₂ initial number densities. The removal amount linearly increases with the initial number density, while the removal rate increases logarithmically. At a lower initial number density, the removal rate is limited. By considering the chemical kinetic mechanism in plasma, a qualitative explanation for the above phenomena is proposed: the additional NO ₂ produced by discharge limits the removal rate, since the NO ₂ concentration is dominated by the competition between the forward reactions (production) and the reverse reactions (removal).