The combination of laser induced Resonance-Enhanced Multi-Photon Ionization and Time-Of-Flight Mass Spectrometry (REMPI-TOFMS) represents a highly selective and sensitive analytical technique ideal for real-time determination of organic trace components. For example, aromatic hydrocarbons can be continuously monitored in industrial off gases. We introduce a new mobile REMPI-TOFMS instrument, which is robust and easy to operate, even under industrial conditions. Instead of an on-line sampling system also a gas chromatograph can be coupled for ultratrace analytical work. The instrument can be equipped with different inlet techniques (effusive inlet, free and skimmed supersonic jet), different TOF mass spectrometric options (linear mode and reflectron mode for higher mass resolution) or different laser systems (robust fixed wavelength lasers or tunable lasers for more sophisticated applications). This flexibility allows the instrument to be readily adapted to a given analytical problem. New time-resolved data of aromatic pollutants in the flue gas from a waste incineration plant is presented. Large fluctuations in the concentrations of combustion by-products were recorded. The presented results show, that a real-time on-line monitoring of hazardous trace chemicals in industrial flue gases is feasible. New possibilities thus arise for innovative environmental protection measures by, amongst others, feed back control of the primary combustion process.