A novel theoretical approach to correct for pathlength amplification and variable sampling loading in measurements of particulate spectral absorption by the quantitative filter technique

Abstract

A simple theoretical model is described that takes into account the combined effects of pathlength amplification and variable sample loading in measurements of particulate spectral absorp- tion by the quantitative filter pad technique. The model differs from previous methods to correct for pathlength amplification by explicitly considering variability in absorptance of sample material on the filter pad, Afp, as a result of different degrees of particle loading on the filter. Functional expressions were evaluated that describe the relationship between Afp and the product of a dimensionless path factor, r, and pathlength amplification factor, b. The path factor, r, represented the product of the absorption coefficient of sample material on the filter and the geometric pathlength of the sample. A simple function was shown to adequately describe the relationship for varying filtration volumes with a variety of sample types, including phytoplankton cultures and coastal waters. Patterns predicted by the model are compared with previously published formulae developed for correction of filter pad absorption measurements. The functional form given here simplifies the approach for determining pathlength amplification.