  We consider Aerosol Index (AI) time-series extracted from TOMS archive for an
area covering Italy $(7-18^o E ; 36-47^o N)$. The missing of convergence in
estimating the embedding dimension of the system and the inability of the
Independent Component Analysis (ICA) in separating the fluctuations from
deterministic component of the signals are evidences of an intrinsic link
between the periodic behavior of AI and its fluctuations. We prove that these
time series are well described by a stochastic dynamical model. Moreover, the
principal peak in the power spectrum of these signals can be explained whereby
a stochastic resonance, linking variable external factors, such as Sun-Earth
radiation budget and local insolation, and fluctuations on smaller spatial and
temporal scale due to internal weather and antrophic components.
