  In this contribution, we develop a model based on classical electrodynamics
that describes light extinction in the presence of arbitrary aerosols. We do
this by combining aerosol and light-intensity measurements performed with the
well-proven measuring systems ELPI+ and MIREX, respectively. The developed
model is particularly simple and depends on only a few input parameters, namely
on densities and refractive indices of the constituting aerosol particles. As
proof of principle, the model is in first applications used to determine
extinction coefficients as well as mass-specific extinction for an infrared
light source with a peak wave length of ${\lambda} = 0.88\ {\mu}m$. In doing
so, detailed studies concentrate on two aerosols exemplary for characteristic
values of the input parameters: a non-absorbing paraffin aerosol in a
bench-scale setup and soot from a flaming n-heptane fire in a room-scale setup
(test fire TF5 according to standard EN54). As main results, we find numerical
values for mass-specific extinction that are first of all different in the two
considered cases. Moreover, obtained results differ in part more than a factor
of three from literature values typically used in practical applications. Based
on the developed model, we explicitly address and assess underlying reasons for
the deviations found. Finally, we propose a simple way how future
light-extinction studies can be performed comparatively easily by means of the
ELPI+-system or measuring devices that work in a similar way.
