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The salient features of the spectral composition of UV radiation at the ground are investigated. A study is made of the degree of influence of the variation of parameters of atmospheric conditions, such as TOC, atmospheric pressure, and aerosol, on the variability of ground-level UV radiation in the region 300-350 nm that manifests itself at Irkutsk. Of them, the most significant were determined in separate bands of the selected range at different time scales. Functions of spectral response of direct midday UVR to variations of atmospheric parameters by 1% of their mean values for Irkutsk were constructed. These functions can be used to assess the influence of actual changes in atmospheric conditions. It is pointed out that the aerosol and cloud state is the factor that determines the overall level of UVR. The effect of pressure fluctuations on UVR variability is insignificant is insignificant; however, in conditions of optical stabilty of the atmosphere, which can persist for several days, the influence of pressure variations on UVR can become of predominant value. TOC and the Sun's altitude are responsible for the spectral composition. For wavelengths longer than 320 nm, it was found that the spectral structure of the UVR variation coefficient coincides with the system of Huggins bands in the ozone absorption spectrum, and for wavelengths shorter than 320 nm, it coincides with typical spectral patterns of the extra-atmospheric solar UV spectrum. It was ascertained that the small-sacle structure of the ground-level spectrum is determined by the structure of the extra-atmospheric solar VU spectrum, while the overall ground-level spectrum is determined by the structure of the extra-atmospheric solar VU spectrum, while the overall spectral variations is determined mainly by the large-scale spectral behavior of the ozone absorption coefficient.
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