Mass and wavelength selected laser excitation is used: (a) for new methods to combine circular dichroism spectroscopy and mass spectrometry of organic molecules. One major application: studies of enantio-selective catalytic processes, (b) to detect traces of air pollutants (e.g. chlorinated PAHs, NOx, SO2, ammonia) for monitoring dynamic combustion and catalytic processes in motorized vehicles; (c) to study molecular systems which are short lived or can only be generated in mixtures (e.g. radicals, ions, clusters) in the isolated gas phase. Example: Chlorine oxides which are dominant at stratospheric ozone depletion; used method: photodetachment-photoelectron spectroscopy.