  In this work, we investigate the role of emission by dust at infrared
wavelengths in the absorption of gamma radiation from distant extragalactic
sources. We use an existing EBL model based on direct starlight emission at
UV/visible and secondary radiation due to dust (PAHs (polycyclic aromatic
hydrocarbons), small and large grains) at IR due to partial absorption of the
stellar component. The relative contribution of each grain type to the total
EBL energy density was determined from a combined fit to the Markarian 501
($z\sim 0.034$) SED in flare state, where both the parameters of the intrinsic
source spectrum and the dust fractions were allowed to vary. By separating the
attenuation due to each EBL component, the importance of individual grain types
to the opacity of the extragalactic medium for the TeV emission of a blazar
like Markarian 501 could be better understood. Using a nested log-likelihood
ratio test, we compared null hypotheses represented by effective 1- and 2-grain
models against a 3-grain alternative scenario. When the temperatures of the
grains are fixed a priori, the 1-grain scenario with only PAHs can be excluded
at more than 5$\sigma$, irrespective of the curvature in the intrinsic
spectrum. The 3-grain EBL model with the tuned fractions was finally used to
fit the SEDs of a sample of extragalactic gamma-ray sources. Such a sample is
still dominated by starlight attenuation, therefore, no statistically
significant improvement in the quality of fits was observed when the tuned
fractions are used to account for the EBL attenuation and the intrinsic
spectrum parameters were allowed to vary during the fit. The potential of this
kind of analysis when the next generation of IACTs, represented by the
Cherenkov Telescope Array, starts observations is enormous. The newly
discovered AGNs at a broad range of redshifts should break many of the
degeneracies currently observed.
