Photoacoustic multicomponent gas analysis using a Levenberg-Marquardt fitting algorithm

A mobile CO2 laser photoacoustic spectrometer has been developed for the in-situ monitoring of atmospheric trace gases in different environments. Numerous air pollutants, such as ammonia, ethene, ozone and alcohols, 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 concentrations from measured photoacoustic signal amplitudes and phases at selected CO2 laser wavelengths. The algorithm has been tested with artificially generated multicomponent gas mixtures exhibiting gas concentrations in the ppb to ppm range. Furthermore, its potential is demonstrated with the analysis of an air sample from a fruit storage chamber and with ambient air measurements during a held study in a rural environment.