Continuous wave cavity ring-down spectroscopy measurement of NO2mixing ratios in ambient air

Abstract

The performance of a continuous wave diode laser based cavity ring-down (CRD) spectrometer is demonstrated for retrieval of NO₂ mixing ratios in ambient air. Measurements are made at wavelengths around 410 nm, a region free from other spectroscopic interferences, and the instrument is shown to be capable of quantitative and precise NO₂ mixing ratio determinations without any requirement for calibration. The minimum concentration of NO₂ that can be measured by the spectrometer is estimated to be 0.1 ppbv (parts per billion by volume) in 50 s at atmospheric pressure. Using dynamic dilution of a standard NO₂ sample, the performance of the spectrometer has been validated for NO₂ measurements over the range of 0.2 to 80 ppbv. NO₂ measurements performed directly on laboratory air are compared with data obtained with a calibrated chemiluminescence instrument and shown to be in excellent agreement.