We present results of many-year studies of the spectral dependence of the atmospheric aerosol optical thickness (AOT) in the spectral region from 0.37–4 μm obtained near Tomsk. In the analysis of the АОT spectral dependence in the short-wave range (< 1 μm), parameters α and β of the Angstrom formula are used while in four spectral intervals between 1.2 and 4 μm of the long-wave range we used the mean value of АОT (τc). Statistical characteristics of α and β variations, as well as of τ0,5 and τc in different seasons and under conditions of the atmosphere polluted with smoke from forest fires are discussed. Mean values of α, β, τ0,5, and τc for the observation period were 1.33, 0.06, 0.153, and 0.055, respectively. Maxima of the aerosol turbidity and selectivity for AOT are observed in spring and during fires, and minima during the fall. Mean value of the wavelength АОT deviations within 1.2–4 μm is 0.02, a small fall of the AOT (about 0.01) is commonly observed within 1–2.2 μm region at increasing wavelength, and then in the region (2–4 μm) a spectrally neutral behavior of the annually mean AOT takes place.