## 3 Results
### Trends
#### 3.3.2 Trends of the Aerosol, Tropospheric NO\({}_{2}\) and Clouds Radiative Effect
However, the trends are statistically significant over the urban location of Volos only where the strongest trend is found (\(-0.80\) W/m\({}^{2}\)/year or \(-1.78\%\)/year), with Olympus and Thessaloniki following (Figure 9c and Figure S15, and Table 3). The negative RE\({}_{\rm lc}\) magnitude trends are not statistically significant except for one location, despite the fact that statistically significant liquid cloud fraction trends are observed over nine locations (Figure S19 and Table 4). The strongest liquid cloud fraction trends are seen over Volos (\(-0.006\)/year or \(-1.88\%\)/year), with Xanthi and Olympus following (\(-0.004\)/year or \(-0.8\) to \(1.2\%\)/year). The effect of the negative liquid cloud fraction trends on RE\({}_{\rm lc}\) is partly counterbalanced by the positive liquid cloud optical thickness trends over some locations (Ioannina, Kozani, Mytilene, Olympus, Orestiada, Pylos, Thessaloniki, and Volos) (see Figure 10c,e and Figure S21, and Table 4). The liquid cloud optical thickness trends are statistically insignificant, ranging from -0.236/year or \(-1.24\%\)/year (Thessaloniki) to 0.188/year or 1.03%/year (Xanthi) (Table 4). Figure 9: Trend of the radiative effect of (**a**) aerosols, (**b**) tropospheric NO\({}_{2}\), (**c**) liquid clouds and (**d**) ice clouds for the period 2005–2019 over 16 locations in Greece. Statistically significant trends at the 95% confidence level are indicated with a cross. Figure 10: Relative trend (to the first year) of **(a)** AOD\({}_{50}\), **(b)** tropospheric NO\({}_{2}\), **(c)** liquid cloud fraction and **(d)** ice cloud fraction, **(e)** liquid cloud optical thickness and **(f)** ice cloud optical thickness for the period 2005–2019 over 16 locations in Greece. Statistically significant trends at the 95% confidence level are indicated with a cross. Aerosol- and cloud-related parameters are from MODIS/Aqua and tropospheric NO\({}_{2}\) from OMI/Aura. Contrary to liquid clouds, the RE\({}_{\rm ic}\) magnitude exhibits positive trends over all the 16 locations except for one (Rhodes). The trends are statistically significant over the rural location of Argos only. Argos exhibits the strongest trend (0.46 W/m\({}^{2}\)/year or 3.57%/year), with Pylos and Olympus following (Figure 9d and Figure S16, and Table 3). The positive RE\({}_{\rm ic}\) magnitude trends follow the positive ice cloud fraction trends. In line with RE\({}_{\rm ic}\), statistical significance is indicated only over Argos, which is the location with the strongest trend (0.003/year or 2.13%/year) along with Volos (0.003/year or 1.70%/year) (Figure S20 and Table 4). Similarly to the case of liquid clouds, the effect of the positive ice cloud fraction trends on RE\({}_{\rm ic}\) is partly counterbalanced by the negative ice cloud optical thickness trends over some locations (Kozani, Mytilene, Olympus, Orestiada, Patras, Preveza) (see Figure 10d,f and Figure S22, and Table 4). The ice cloud optical thickness trends are statistically insignificant except for Pylos, ranging from \(-0.218/\)year or \(-1.01\%/\)year (Olympus) to 0.615/year or 5.53%/year (Pylos) (Table 4). Concluding, among the parameters that are studied here, AOD\({}_{550}\) and liquid cloud fraction drive the positive SSR trends observed in the area. These parameters generally decreased over the area within the period 2005-2019, while, on the contrary, the ice cloud fraction increased, exhibiting an opposite radiative effect change. Also, for some stations,  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Location** & **AOD\({}_{550}\)** & **Trop.