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Absorption coefficient, a, of light in a medium is related to the concentration in that medium of the light-absorption agent, as well as to optical properties of the agent. Hence, by normalizing a to the concentration of that agent, one should be able to focus on the effect of those properties on light absorption by the medium. This leads to the concept of the concentration-specific absorption coefficient, exemplified by the mass-specific absorption coefficient and the molar absorption coefficient.
The mass-specific absorption coefficient [length2 mass-1] is defined as follows:
| am = a / Cmv | (1) |
where a is the absorption coefficient defined by Eq 1 in Absorption coefficient, and Cmv [mass length-3] is the mass-per-volume concentration of the light absorbing agent. That agent can be dissolved in the medium, and/or dispersed as particles.
In aquatic sciences, the mass-specific absorption coefficients include the particle mass-specific absorption coefficient, ap*, (for example, Woźniak SB et al 2010) or the chlorophyll-specific absorption coefficient, achl*, (for example, Bricaud A et al 1995) and are typically expressed in m2 g-1 and m2 mg-1, respectively.
The molar absorption coefficient, usually expressed in dm3 moles-1 cm-1 in the spectroscopic literature (for example, Braslavsky SE 2007), is defined as follows:
| aM = a / CM | (2) |
where a is the absorption coefficient defined by Eq 1 in Absorption coefficient, and CM [moles dm-3] is the molar concentration of the light absorbing agent.
Given that the volume per unit mass of a medium is temperature dependent, the concentration-specific absorption coefficients also depend on temperature.
| CITATION: Jonasz M. 2009. Absorption coefficient: concentration-specific (www.tpdsci.com/Tpc/AbsCfSpc.php). In: Top. Part. Disp. Sci. (www.tpdsci.com). |
HISTORY: Published: -2009 Modified: 28-Jan-2009 Peer-reviewed: 16-May-2011 |
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