Data of many-year (1992-2007) observations of atmospheric transparency in the region of Tomsk city are used to analyze spectral features of the inter-annual variations of aerosol optical thickness (AOT) in the visible and near-IR spectral ranges. We present statistical characteristics of the spectral AOT and Angstrom parameters, as well as discuss the causes of their inter-annual variations. Results of comparison with data from other regions in the post-volcanic (after 1994) period have shown the absence of a significant trend and a small difference of AOT in three quite different regions of Russia (Moscow, Bugrino, and Tomsk). For the Moscow region, we discuss characteristics of the trend for a longer time period, from 1955 to 2007. It is shown that there is no direct significant relation to the cycles of the solar activity in many-year AOT variations in all considered regions.
aerosol-optical depth, trend, volcanoes