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
R. A. Rooth, A. J. L. Verhage, and L. W. Wouters, "Photoacoustic measurement of ammonia in the atmosphere: influence of water vapor and carbon dioxide," Appl. Opt. 29, 3643-3653 (1990)