Biological aerosols like pollen or bacteria can be differentiated from non-biological aerosols as dust by fluorescence. Several organic substances contained in biological particles emit fluorescence light if they are illuminated with ultraviolet light. An instrument has been developed which generates aerosols of individual bacteria. illuminates them with light in the range of wavelengths from 2210 to 570 nm and detects the spectra of fluorescence. The instrument has been tested on different species of bacteria showing that their fluorescence spectra are different.