Abstract

The photoacoustic determination of the ammonia concentration in atmospheric air by absorption of CO₂ laser radiation at 9.22 μm is influenced by the presence of H₂O and CO₂. Kinetic cooling due to the coupling of excited CO₂ and N₂ levels causes important changes in phase and amplitude of the photoacoustic signal. Theoretical background is presented to deduce the correct NH₃ concentration from the signal. The experimental setup used to perform field measurements is described. Adhesion of NH₃ to the walls of the resonant photoacoustic cell was investigated. Temperature effects are treated. Field data of NH₃ and H₂O concentrations are presented.

© 1990 Optical Society of America

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