The results of simulation of the influence of inhomogeneity in the spatial structure of aerosol field on the observed optical characteristics of the propagation path (its optical thickness or the effective extinction coefficient determined on its basis) are analyzed. It is shown that the random distribution of aerosol characteristics leads to the biased estimates of the average atmospheric optical thickness. In the case in which the spatial aerosol distribution is described by fractal regularities, a polymodal character of the probability of the optical thickness observation is revealed.