Diode laser photoacoustic detection of automobile exhaust emissions

A study of the infrared spectra of the CH/sub 4/, NH/sub 3/, N/sub 2/O and ethane gases has been carried out. These molecules are part of atmospheric pollution caused by emissions from automobile traffic. We tested the method of photoacoustic (PA) detection together with the laser semiconductor emission as a new tool for monitoring of limited concentrations of these atmospheric pollutants. The variation of the intensity of the PA signal with pressure was studied. The detection limits were determined for the individual gases in mixtures with air at the optimum pressure. The spectra of automobile exhaust gases at various motor temperatures were measured qualitatively and quantitatively. A new type of semiconductor GaInAsSb/AlGaAsSb laser, working in the 4342-4362 cm/sup -1/ region at room and higher temperatures, was used as the tunable radiation source.