Long-Term Variability of UV Irradiance in the Moscow Region according to Measurement and Modeling Data

We have found distinct long-period changes in erythemal UV radiation (Q(er)) characterized by a pronounced decrease at the end of the 1970s and a statistically significant positive trend of more than 5%/10 years since 1979 over the territory of the Moscow region according to the measurements and reconstruction model. The positive Q(er) trend is shown to be associated mainly with a decrease in the effective cloud amount and total ozone content (TOC). Due to these variations, UV resources have significantly changed in spring for the population with the most vulnerable skin type I, which means a transition from the UV optimum to UV moderate excess conditions. The simulation experiments using the INM-RSHU chemistry climate model (CCM) for several scenarios with and without anthropogenic factors have revealed that the variations in the anthropogenic emissions of halogens have the most significant impact on the variability of TOC and Q(er). Among natural factors, noticeable effects are observed due to volcanic aerosol. The calculations of the cloud transmittance of Q(er) are generally consistent with the measurements; however, they do not reproduce the observed value of the positive trend.