Assessing aerosol-related uncertainties in satellite-based retrievals of effective UV doses for the production of cutaneous vitamin D.  

Solar Ultraviolet (UV) radiation plays a key role in many chemical and biological processes, and affects significantly human health. Excessive UV exposure may lead to adverse health effects, including sunburns, skin cancer, and cataracts, whereas moderate exposure is beneficial, e.g., by supporting vitamin D production and promoting mental well-being, among other benefits. UV radiation interacts with various atmospheric components before reaching the Earth’s surface. Photons with shorter wavelengths are absorbed at higher atmospheric layers by oxygen and tropospheric ozone, and practically only UV-A and a small part of the UV-B irradiance reach the troposphere. In the troposphere, UV is scattered by air molecules and is further attenuated by aerosols and clouds. Interactions between UV radiation and aerosols are not yet completely understood, and their parameterization constitutes a major uncertainty factor in models and satellite retrieval algorithms. Understanding these interactions is thus essential for accurately assessing UV exposure using modeled UV irradiance.Τhe purpose of this study is to evaluate satellite- and reanalysis-based retrievals of the effective dose for the cutaneous vitamin D synthesis using ground-based measurements over Athens and Thessaloniki, Greece. We evaluate data that are derived (1) using the methodology described in Fragkos et al., (2024, https://doi.org/10.3390/rs16111878), based on CAMS information in combination with satellite data from OMI and MSG, and (2) the UV climatology of which is also based on data from various sensors analyzing air quality. Ground-based spectral solar UV irradiance measurements performed with a MKIV single monochromator Brewer spectrophotometer in Athens, and a MKIII double monochromator Brewer spectrophotometer in Thessaloniki are used to validate the Satellite-based retrievals. AOD measurements from co-located CIMEL sun-photometers, part of the AERONET network are used to assess the effect of aerosols. The evaluation has been performed for the period 2004 - 2024. Further analysis yielded positive trends in the effective dose for vitamin D production in the last two decades, mainly due the decreasing trends in aerosols.