This paper reports on the development of a compact analyzer for ammonia monitoring in air, based on a distributed feedback diode laser at 2.005 mu m. A dual-beam long-path technique was combined with wavelength modulation detection of absorption in order to reach a detection limit of about 25 ppb, with a 0.2-Hz equivalent noise bandwidth. Retrieval of NH3 concentration was accomplished through a careful spectra analysis procedure based on the formalism of Fourier expansion of the 2nd harmonic signals, also taking into account residual-amplitude-modulation effects. The system was tested on certified gas-mixtures and revealed a good performance in terms of accuracy and reproducibility. Particularly, the short-term precision was found to be about 1 parts per thousand, for NH3 mixing ratios of 10 ppm. Finally, the possibility to make use of the analyzer for measurements of ammonia fluxes from soils is discussed.
High precision determinations of NH3 concentration by means of diode laser spectrometry at 2.005 mu m
De Tommasi E;
2006
Abstract
This paper reports on the development of a compact analyzer for ammonia monitoring in air, based on a distributed feedback diode laser at 2.005 mu m. A dual-beam long-path technique was combined with wavelength modulation detection of absorption in order to reach a detection limit of about 25 ppb, with a 0.2-Hz equivalent noise bandwidth. Retrieval of NH3 concentration was accomplished through a careful spectra analysis procedure based on the formalism of Fourier expansion of the 2nd harmonic signals, also taking into account residual-amplitude-modulation effects. The system was tested on certified gas-mixtures and revealed a good performance in terms of accuracy and reproducibility. Particularly, the short-term precision was found to be about 1 parts per thousand, for NH3 mixing ratios of 10 ppm. Finally, the possibility to make use of the analyzer for measurements of ammonia fluxes from soils is discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
