An instrument used to measure the intensity and the @[email protected] distribution of the light emitted as @[email protected] from a molecule excited at a specific @[email protected] or wavelengths within the absorption band of a particular compound. Characteristic @[email protected] bands may be used to identify specific pollutants such as the polynuclear aromatic @[email protected] Excitation spectra of impurities can be observed by scanning the @[email protected] of the excitation light which is incident on the sample over a range of wavelengths and observing the relative intensity of the @[email protected] emitted at a given @[email protected] These spectra are also characteristic of the impurity.