## 5 Conclusions
; validation, G.A. and A.K.G. ; formal analysis, G.A. and A.K.G. ; investigation, G.A., A.K.G. and D.B. ; resources, G.A., A.K.G. and D.B. ; data curation, G.A. and A.K.G. ; writing--original draft preparation, G.A. and A.K.G. ; writing--review and editing, G.A., A.K.G. and D.B. ; visualization, G.A. and A.K.G. ; supervision, D.B. ; project administration, D.B. ; funding acquisition, G.A., A.K.G. and D.B. All authors have read and agreed to the published version of the manuscript. This research was co-financed by Greece and the European Union (European Social Fund-ESF) through the Operational Program +Human Resources Development, Education and LifelongLearning 2014-2020* in the context of the project \"Long-term variability of solar radiation in Greece: effect of air quality and clouds\" (MIS 5047844). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The data that emerged from this research, along with the corresponding computational tools, can be available from the corresponding author on request. The MODIS/Aqua level-2 joint atmosphere product (MYDATML2; doi:10.5067/MODIS/MYDATML2.061) is publicly available through NASA's Goddard Space Flight Center (GSFC) Level-1 and Atmosphere Archive and Distribution System (LAADS; [[https://ladsweb.modaps.esosdis.nasa.gov/](https://ladsweb.modaps.esosdis.nasa.gov/)]([https://ladsweb.modaps.esosdis.nasa.gov/](https://ladsweb.modaps.esosdis.nasa.gov/)), accessed on 30 June 2021). The QA4 ECV tropospheric NO\({}_{2}\) column data from the OMI sensor (doi:10.21944/qa4 ecv-no2-omi-v1.1) are publicly available from KNMI's Tropospheric Emission Monitoring Internet Service (TEMIS; [[http://www.temis.nl](http://www.temis.nl)]([http://www.temis.nl](http://www.temis.nl)), accessed on 30 June 2021). The MACv2 aerosol climatology data are freely available via [[ftp://ftp-projects.mpimet.mpg.de/aerocom/climatology/MACv2_2018/](ftp://ftp-projects.mpimet.mpg.de/aerocom/climatology/MACv2_2018/)]([ftp://ftp-projects.mpimet.mpg.de/aerocom/climatology/MACv2_2018/](ftp://ftp-projects.mpimet.mpg.de/aerocom/climatology/MACv2_2018/)), accessed on 30 June 2021. The CALIOP/CALIPSO v4.20 monthly level-3 aerosol profile data (doi:10.5067/CALIOP/CALIPSO/CAL_LID_L3_Tropospheric_APro_CloudFree-Standard-V4-20) are publicly available from NASA's Langley Research Center Atmospheric Science Data Center via [[https://search.earthdata.nasa.gov/](https://search.earthdata.nasa.gov/)]([https://search.earthdata.nasa.gov/](https://search.earthdata.nasa.gov/)), accessed on 30 June 2021. The CM SAF SARAH-2.1 surface solar radiation (SSR) data (doi:10.5676/ EUM_SAF_CM/SARAH/V002_01) are publicly available via the Satellite Application Facility on Climate Monitoring (CM SAF; [[https://www.cmsaf.eu](https://www.cmsaf.eu)]([https://www.cmsaf.eu](https://www.cmsaf.eu)), accessed on 30 June 2021). The CERES EBAF edition 4.1 data (CERES_EBAF_Ed4.1; doi:10.5067/Terra-Aqua/CERES/EBAF_L3B_004.1) are publicly available from NASA's Langley Research Center CERES ordering tool at [[https://ceres.larc.nasa.gov/](https://ceres.larc.nasa.gov/)]([https://ceres.larc.nasa.gov/](https://ceres.larc.nasa.gov/)), accessed on 30 June 2021. The ground-based SSR observations from Thessaloniki, Athens and HCMR were obtained from LAP/AUTH, IESRD/NOA and HCMR upon request. The OMI/Aura O\({}_{3}\) total column dataset (OMTO3d version v3; doi:10.5067/Aura/OMI/DATA3001) is publicly available via [[https://search.earthdata.nasa.gov/](https://search.earthdata.nasa.gov/)]([https://search.earthdata.nasa.gov/](https://search.earthdata.nasa.gov/)), accessed on 30 June 2021. The CM SAF CLARA-A2.1 surface albedo (doi:10.5676/EUM_SAF_CM/CLARA_AVHRR/V002_01) and CLAAS-2.1 cloud (doi:10.5676/EUM_SAF_CM/CLAAS/V002_01) data are publicly available via the CM SAF website ([[https://www.cmsaf.eu](https://www.cmsaf.eu)]([https://www.cmsaf.eu](https://www.cmsaf.eu)), accessed on 30 June 2021).