A method used to detect and identify biological substances suspended in air in the form of aerosols or clouds including generating a remote infrared light beam directed toward the atmospheric contamination, producing an ultraviolet light beam from the infrared light beam by compression via the air through which the IR beam travels, and producing fluorescence of the atmospheric contamination, when the generated ultraviolet light contacts the atmospheric contamination. The fluorescent signals are then processed in order to identify the nature of the atmospheric contamination.