Photoacoustic spectroscopy (PAS) with tunable IR lasers represents a p
romising tool for trace gas monitoring. The principles of PAS applied
to multicomponent gas mixtures are briefly outlined. We present three
photoacoustic (PA) systems and discuss typical results. A CO laser PA
system has been applied to the selective analysis of volatile organic
compounds (VOCs) in motor vehicle exhausts and to the study of the dim
erization of fatty acid vapors. As a second instrument, an automated m
obile CO2 laser PA system has been employed for in situ air monitoring
in industrial, urban and rural environments. A detection limit in the
ppb-range can be achieved depending on molecular absorption cross sec
tions and absorption interferences. Despite some cases which demonstra
te the feasibility to differentiate even between isomers, the detectio
n selectivity could often be substantially improved by employing a con
tinuously rather than a line-tunable laser source. This is demonstrate
d by our high-pressure CO2 laser which offers continuous tunability in
the common CO2 laser emission branches with a linewidth of only 0.017
cm(-1). Other approaches that we presently pursue include the use of
CO2 laser isotopes, measurements with a PA Stark cell for monitoring a
mmonia and, finally, spectrometers with tunable MIR lasers based on op
tical parametric oscillation (OPO) or difference frequency generation
in nonlinear optical crystals as sources.