Photoacoustic measurement of N2O concentrations in ambient air with a pulsed optical parametric oscillator

Abstract

Photoacoustic spectroscopy, in combination with a pulsed grazing-incidence optical parametric oscillator (GIOPO), was used for sensitive detection of nitrous oxide (N2O) in ambient air. The ν1+ν3 combination band of N2O was excited with the idler beam of the GIOPO in the 2.76 μm–2.91 μm spectral region, where CO2 and water-absorption lines are also present. Three chemical filters filled with KOH, CaCl2, and P2O5 were used to reduce the CO2 and water concentrations to the level of several parts per billion (109) by volume (ppbv). Photoacoustic spectra containing several absorption lines were recorded and the concentration was determined by an integral evaluation method and a fast Fourier transform evaluation method. The photoacoustic signal was calibrated by a standard mixture of 50.6 parts per million by volume (ppmv) of N2O in synthetic air. Values of 311±5 ppbv, 314±5 ppbv, and 316±5 ppbv were found for three ambient samples collected at nearby roads.