Photoacoustic measurement of ammonia in the atmosphere: influence of water vapor and carbon dioxide

Abstract

The photoacoustic determination of the ammonia concentration in atmospheric air by absorption of CO(2) laser radiation at 9.22 microm is influenced by the presence of H(2)O and CO(2). Kinetic cooling due to the coupling of excited CO(2) and N(2) levels causes important changes in phase and amplitude of the photoacoustic signal. Theoretical background is presented to deduce the correct NH(3) concentration from the signal. The experimental setup used to perform field measurements is described. Adhesion of NH(3) to the walls of the resonant photoacoustic cell was investigated. Temperature effects are treated. Field data of NH(3) and H(2)O concentrations are presented.