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The influence of different factors on the total ozone content (TOC) and erythemal UV radiation (Qery) in the atmosphere over northern Eurasia from 1979 to 2059 has been analyzed using a chemistry-climate model developed at the Institute of Numerical Mathematics (INM, Russian Academy of Sciences) and the Russian State Hydrometeorological University (RSHU). The sensitivity of modeled ozone contents to different input data on sea-surface temperature (SST) has been estimated. The TOC trends may significantly differ depending on the SSTs used. The results of the model experiment, which takes into account variations in the anthropogenic emissions of halogen-containing substances, suggest a nonlinear Qery decrease due to the recovery of the ozone layer in the 21st century. The values of Qery for 2016–2020 are 2–5% higher than its values for 1979–1983, on average, for all of northern Eurasia (with its maximum on the order of 6% in the polar latitudes). The Qery values equalize in 2035–2039 and then gradually decrease (when compared to those for 1979–1983) by 4–6% for Asia and 6–8% for northern Europe in 2055–2059. Therefore, variations are observed in the spatial distribution of UV resources, which are most significant in spring and summer: these variations are manifested in the extension of UV-deficiency zones in the north and the reduction of UV-excess zones in the south. [ABSTRACT FROM AUTHOR]

Temporal variability in erythemal radiation over Northern Eurasia (40°–80° N, 10° W–180° E) due to total ozone column (X) and cloudiness was assessed by using retrievals from ERA-Interim reanalysis, TOMS/OMI satellite measurements, and INM-RSHU chemistry–climate model (CCM) for the 1979–2015 period. For clear-sky conditions during spring and summer, consistent trends in erythemal daily doses (Eery) up to +3%/decade, attributed to decreases in X, were calculated from the three datasets. Model experiments suggest that anthropogenic emissions of ozone-depleting substances were the largest contributor to Eery trends, while volcanic aerosol and changes in sea surface temperature also played an important role. For all-sky conditions, Eery trends, calculated from the ERA-Interim and TOMS/OMI data over the territory of Eastern Europe, Siberia and Northeastern Asia, were significantly larger (up to +5–8%/decade) due to a combination of decrease in ozone and cloudiness. In contrast, all-sky maximum trends in Eery, calculated from the CCM results, were only +3–4%/decade. While Eery trends for Northern Eurasia were generally positive, negative trends were observed in July over central Arctic regions due to an increase in cloudiness. Finally, changes in the ultraviolet (UV) resources (characteristics of UV radiation for beneficial (vitamin D production) or adverse (sunburn) effects on human health) were assessed. When defining a "UV optimum" condition with the best balance in Eery for human health, the observed increases in Eery led to a noticeable reduction of the area with UV optimum for skin types 1 and 2, especially in April. In contrast, in central Arctic regions, decreases in Eery in July resulted in a change from "UV excess" to "UV optimum" conditions for skin types 2 and 3. [ABSTRACT FROM AUTHOR]