Marine Science Faculty Publications

Absorbance, Absorption Coefficient, and Apparent Quantum Yield: a Comment on Common Ambiguity in the Use of These Optical Concepts

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Several important optical terms, such as "absorbance" and "absorption coefficient," are frequently used ambiguously in the current peer-reviewed literature. Because these terms are important when deriving other quantities, such as the apparent quantum yield of photoproduction, ambiguity in the application of these concepts leads to results that are difficult or impossible to interpret correctly. Such ambiguity also hinders comparison of results between studies and ultimately harms proper parameterization of numerical models of oceanic processes, as well as the refinement of remote sensing algorithms. We review these concepts and the implications of such ambiguities. A few simple recommendations that follow conventions developed by optical oceanographers are provided to authors dealing with these concepts. In particular, the symbol a is recommended for the absorption coefficient (in Napierian form, m -1 ), which is also preferred over absorbance (dimensionless) when data are presented; the symbol a is not recommended for absorbance; A should be used with caution because, although it has been used widely for absorbance in photochemistry and photobiology, it has also been used for absorptance in physics and optical oceanography; the term "absorptivity" is not recommended because of conflicting definitions in the current literature; the pathlength should always be given whenever absorbance data are presented; and normalization of photoproduction rates to absorbance or absorption coefficient should be performed only on optically thin samples, unless the inner filter effects are accounted for and corrected.

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Limnology and Oceanography, v. 47, issue 4, p. 1261-1267