Using several arrays of the aerosol extinction coefficients α(λ) as an example, it is shown that the coefficients α(λ) can be statistically separated into components caused by particles of different size in a wide spectral range. For separation, the apparatus of linear multivariate regression analysis is applied. It is shown, in particular, that the component of α(λ) caused by particles of the fine-disperse fraction not only contributes in the visible spectral range (due to scattering), but also shows itself in the infrared spectral range (due to absorption). This approach allows statistical detection of the weak atmospheric absorption in the spectral range λ > 9 mm in the real atmosphere. The character of the spectral dependence suggests that it is caused by radiation absorption by small water particles, which are optically inactive in the visible spectral range.