Improving satellite-based estimations of UV index and dose and first assessment of UV in a world-avoided
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The UV index (UVI) and dose (UVD) are quantities of UV irradiance weighted for its effect on organisms. Both quantities are widely used as informative tools or as proxies for UV irradiance, commonly used in e.g. skin cancer research. The UVI and UVD can be measured using groundbased spectrometers, or modelled using satellite observations of ozone. The Royal Netherlands Meteorological Institute has developed a UV model with a unique spatial and temporal coverage. This study describes the update of this model. Updates include changing the computation and data sets used, regarding: ground elevation, surface albedo, cloud cover and error estimation. The updated model is used to compute UVI and UVD from the long-term Multi-Sensor Reanalysis of ozone, and compared with ozone fields that would have been present if the 1987 Montreal Protocol had not been adopted. We find that the northern hemisphere ozone depletion event of 2011, which is greatly exaggerated in absence of the Montreal Protocol, has only little effect on UV irradiance. Comparing scenarios with and without Montreal Protocol, we find that by the year 2012 the implementation of the Montreal Protocol has prevented UV levels from shifting nearly 10 degrees poleward in summer, an increased global sunburn rate by 9.9%, while also preventing a 14.5% increase in (sun related) vitamin D production. For UVD thresholds relevant for vitamin D sufficiency, we found an order of magnitude estimation of the effect of the Montreal Protocol: Removing part of the ozone layer, which the Montreal Protocol prevented, has a similar effect on surface UV irradiance as removing all cloud cover throughout the year.