PHOTOACOUSTIC MULTICOMPONENT GAS-ANALYSIS USING A LEVENBERG-MARQUARDTFITTING ALGORITHM

A mobile CO2 laser photoacoustic spectrometer has been developed for t he in-situ monitoring of atmospheric trace gases in different environm ents. Numerous air pollutants, such as ammonia, ethene, ozone and alco hols, can be monitored with a time resolution of a few minutes. A new fitting algorithm based on the numerical method of Levenberg-Marquardt is discussed and applied to the derivation of individual gas concentr ations from measured photoacoustic signal amplitudes and phases at sel ected CO2 laser wavelengths. The algorithm has been tested with artifi cially generated multicomponent gas mixtures exhibiting gas concentrat ions in the ppb to ppm range. Furthermore, its potential is demonstrat ed with the analysis of an air sample from a fruit storage chamber and with ambient air measurements during a held study in a rural environm ent.