Variability of the amplification factor of light absorption by filter-retained aquatic particles in the coastal environment

The amplification of light absorption by aquatic particles retained on glas s-fiber filters, the so-called beta factor, has been measured for 29 statio ns located in the varying coastal environment of the northern basin of the Adriatic Sea. The spectral values of the optical density of particles have been determined on glass-fiber filters by the standard transmittance (T) me thod as well as by the transmittance-reflectance (T-R) method, which perfor ms an accurate correction for light backscattering by the particles, and on glass slides by the modified filter-transfer-freeze (FTF) method, which el iminates the pathlength amplification. It has been shown that the relations hips between the optical densities of particles on glass slides (ODsus) and on glass-fiber filters (ODf) have a low dispersion when ODf is measured by the T-R method: in this case, the use of a single expression for all stati ons adds an error that does not exceed the typical uncertainty of the measu rement of the filter-retained particle absorption. On the contrary, the ODs us versus ODf plots obtained by the T method exhibit considerable variabili ty, apparently due to the approximate correction for light backscattering p erformed by this method, and do not permit the use of a single equation for all stations.