Unlike some other satellite-based models, which use monthly averages of aerosol data as input, the SolarGIS model uses daily values of aerosol inputs. As aerosols are highly variable in time, use of daily aerosol data helps us to better represent day-by-day variability and occurrence of extreme irradiation values.
A nice example that shows why use of daily aerosol values (instead of monthly averages) is important for high-quality solar resource modelling can be seen in the following animation: http://www.gmes-atmosphere.eu/pressroom/macc_dust_sr4.gif
In this example it shown how plumes of desert dust from the Sahara impact areas as far as Central Europe. It would not be possible to capture the rapidly changing aerosol conditions over South Europe and North Africa if daily values of aerosol are not used.