Pulsed-cavity ring down spectroscopic study of NO2 in 501–506 nm spectral region

Abstract

Cavity ring-down spectroscopy (CRDS) is a highly sensitive laser absorption spectroscopic technique. In this paper, we report the pulsed CRDS study of nitrogen dioxide (NO2) using an home-built CRDS set-up. Pulsed CRDS measurements of diluted NO2 gas (0.091% in N2) at various low pressures have been carried out in 501–506 nm spectral range. From the CRDS measurements, molecular spectral features of NO2 at very low partial pressure, ∼10 mTorr (3.42 × 1014 molecules/cm3), was evidently observed. CRDS ring-down decay measurements carried out at wavelength of 504.76 nm for various molecular concentrations of NO2 demonstrate a minimum detectable number density of NO2 of 8.65 × 1012 molecules/cm3, which would correspond to 350 ppbv under atmospheric condition. 40 ppbv of detection limit of NO2 is estimated from the standard deviation (1σ) of ring-down decay time measurements at 504.76 nm wavelength. Absorption and integrated absorption cross section of NO2 are also estimated.