Long-term measurements of erythemally weighted UV irradiance (<i>Q</i><sub>er</sub>) have been analyzed for the 1999–2006 period as well as UV variability according to reconstruction model since 1968. The estimates of different atmospheric parameters effects, including NO<sub>2</sub> content, on <i>Q</i><sub>er</sub>) have been obtained on seasonal and interannual scales. It has been shown that NO<sub>2</sub> content in conditions of large megalopolis provides average <i>Q</i><sub>er</sub> decrease of about 1.5–2%. The seasonal variations of the observed UV indices are discussed from the point of view of the impact on health. Using the reconstruction model we showed a distinct growth in <i>Q</i><sub>er</sub> since 1980 due to decrease in total ozone (+2.5% per decade), effective cloud amount transmission (+2.1% per decade) and aerosol loading (+1.1% per decade). However, there is no changes in <i>Q</i><sub>er</sub> over larger 1968–2006 period due to significant decrease in effective cloud amount transmission (−11% per decade) in 1968–1980.