## 5 Conclusions
\(\rm RE_{\rm lc}\) is very low in the summer (July and August), ranging from \(-2\) to 0 W/m\({}^{2}\) for 9 out of the 16 locations. The highest \(\rm RE_{\rm lc}\) value appears in May over Ioannina (\(-44\) W/m\({}^{2}\));
* Positive SSR trends (increase), ranging from 0.01 W/m\({}^{2}\)/year (Rhodes) to 0.52 W/m\({}^{2}\)/year (Olympus), appear over all the locations for the period 2005-2019, except for two, which are Mytilene (\(-0.27\) W/m\({}^{2}\)/year or \(-0.14\%\)/year) and HCMR (\(-0.12\) W/m\({}^{2}\)/year or \(-0.06\%\)/year). Over the two locations with the strongest trends, Volos (0.78 W/m\({}^{2}\)/year or 0.45%/year) and Thessaloniki (0.67 W/m\({}^{2}\)/year or 0.40%/year), the trends are statistically significant at the 95% confidence level. Our SSR trends, in general, agree with those of CM SAF (2005-2017) and CERES (2005-2019), indicating an increase in SSR over Athens and Thessaloniki, which is in agreement to the ground observations;
* The general decrease in AOD\({}_{550}\) (trends ranging from \(-0.005\)/year to zero depending on the location) and liquid cloud fraction (trends ranging from \(-0.006\)/year to \(-0.001\)/year) drives the positive SSR trends observed in the area for the period 2005-2019. The strongest \(\rm RE_{\rm aer}\) magnitude trends appear over the urban locations of Patras (\(-0.35\) W/m\({}^{2}\)/year or \(-1.74\%\)/year) and Thessaloniki (\(-0.31\) W/m\({}^{2}\)/year or \(-2.05\%\)/year), and the strongest \(\rm RE_{\rm lc}\) magnitude trend is found over the urban location of Volos (\(-0.80\) W/m\({}^{2}\)/year or \(-1.78\%\)/year). These three trend values are statistically significant at the 95% confidence level;
* The effect of tropospheric NO\({}_{2}\) on the SSR trends is negligible. Negative \(\rm RE_{\rm NO2}\) magnitude trends (statistically significant for some locations only) are found over all the locations except for one (Antikythera). The negative \(\rm RE_{\rm NO2}\) magnitude trends reflect the negative trends of tropospheric NO\({}_{2}\). The strongest tropospheric NO\({}_{2}\) trends (also statistically significant) are seen over the urban locations of Kozani (\(-0.21\times 10^{15}\) molecules/cm\({}^{2}\)/year or \(-395\%\)/year), Athens (\(-0.19\times 10^{15}\) molecules/cm\({}^{2}\)/year or \(-3.57\%\)/year), and Thessaloniki (\(-0.11\times 10^{15}\) molecules/cm\({}^{2}\)/year or \(-2.89\%\)/year);
* Contrary to liquid clouds, the \(\rm RE_{\rm lc}\) magnitude exhibits positive trends over all the locations except for one (Rhodes). Argos exhibits the strongest trend (0.46 W/m\({}^{2}\)/year or 3.57%/year), being also the only location with a statistically significant trend. The positive \(\rm RE_{\rm lc}\) magnitude trends follow the positive ice cloud fraction trends (ranging from zero to 0.003/year depending on the location);
* The liquid and ice cloud optical thickness has increased for some stations, while for others it has decreased during 2005-2019, suppressing or boosting the changes in the radiative effect of clouds, which are induced by changes in the liquid and ice cloud fractions. This study highlights the driving role of clouds and aerosols in the solar radiation levels reaching the Earth's surface. Tropospheric NO\({}_{2}\) may exert a significant radiative effect on SSR on an annual basis, only over the most heavily polluted areas of the world (e.g., Eastern China). However, under episodic events (e.g., extended forest or agricultural fires), the instantaneous radiative effect of tropospheric NO\({}_{2}\) might be considerable on a local or regional scale. This is something that merits further investigation. The following are available online at [[https://www.mdpi.com/article/10.3390/rs13132587/s1](https://www.mdpi.com/article/10.3390/rs13132587/s1)]([https://www.mdpi.com/article/10.3390/rs13132587/s1](https://www.mdpi.com/article/10.3390/rs13132587/s1)), a document with Figures S1-S23 and their captions: Electronic Supplement. Conceptualization, G.A., A.K.G. and D.B. ; methodology, G.A., A.K.G. and D.B. ; software, G.A. and A.K.G.