The fluorescence emitted by aerosol particles is registered by the UVAPS in one of 64 channels, depending on the intensity of the signal. The UVAPS does not provide the nominal values for the fluorescence intensity of the particles in arbitrary units such as relative fluorescence units (rfu), as is typically reported by the spectrophotometers. Instead, the intensity of the signals is reported on a scale from 1 to 64, corresponding to the channel numbers. Accordingly to the Beer-Lambert law, the fluorescence intensity should be directly proportional to the amount of fluorophores in the aerosol particles, in the absence of quenching. In order to facilitate interpretation of the UVAPS data in regard to the composition of airborne biological particles, a linearity of the fluorescent signals of the spectrometer was investigated
