Single Scattering Properties

Three properties are required to exactly specify the radiative effects of particles. The properties define the total extinction (scattering plus absorption) due to the particle, the probability of an interaction resulting in absorption than scattering, and, finally, the angular distribution of scattered photons as a function of the incident angle. By convention, the properties defining the above attributes are usually specified as the extinction optical depth $\tauext$, the single scattering albedo $\ssa$, and the asymmetry parameter $\asmprm$. These three parameters, $\tauext$, $\ssa$, and $\asmprm$, are known collectively as the single scattering properties of the particles. These properties depend in turn on the mass, size, and composition of the particle species.

The particles chemical composition determines its index of refraction $\idxrfr$, which is expressed as a complex number

$$\idxrfr = \idxrfrrl + \idxrfrimg \iii$$ (97)

All the physics describing the fundamental electromagnetic properties of the material are consolidated into $\idxrfr$. $\idxrfrrl$ describes the scattering properties of the medium while $\idxrfrimg$ describes the absorption properties of the medium. There is disagreement in the literature about the appropriate sign of $\idxrfrimg$. This is a matter of convention and we choose to represent as positive definite, i.e., $\idxrfrimg > 0$. This is the convention adopted by , among others.

$\idxrfrrl$ and $\idxrfrimg$ are fundamental properties of matter and must be determined from laboratory studies . The HITRAN database contains a compilation of $\idxrfr$for most aerosols of atmospheric interest.

contains a compilation of $\idxrfr$for most aerosols of atmospheric interest.