\subsection{Tropospheric Ultraviolet and Visible radiative transfer model}
\label{TUV}

The solar spectrum was also calculated using the Tropospheric Ultraviolet Visible radiation model (TUV) developed by Madronich, 1993. The source code (Available at http://acd.ucar.edu/UV/) solves the radiative transfer equation by applying the discrete-ordinates algorithm (DISORT) \cite{Stamnes1988}. The optical properties of the atmosphere depend on its altitude and composition features (aerosols, ozone profile, cloud cover, water vapor and other gases). TUV algorithm divides the atmosphere in homogeneous layers and assumes constant scattering and absorption in each of them. The intensity solar radiation able to reach the Earth’s surface varies depending also on the seasons, geographic location, soil reflectivity, etc. 

The most important inputs to TUV model are: date, local time, location (latitude, longitude and height above sea level), total ozone column, aerosol optical depth at 550 nm, the Ångström coefficient, surface albedo, single-scattering albedo, interval wavelength and spectral resolution \cite{Madronich1993}. In order to determine $E^{S}_{\lambda}$ in clear sky days, all parameters mentioned above were considered into the code.

Ozone values were taken from measurements of the Ozone Monitoring Instrument (OMI) on board NASA's EOS-AURA satellite. OMI was designed by NASA in collaboration with the Netherlands's Agency for Aerospace Programs (NIVR) and the Finnish Meteorological Institute (FMI). The data are available from Goddard Space Flight Center (GSFC/DAAC). We have considered the data over a satellite pixel to La Plata city coordinates. At the same time, the data base corresponding to the aerosol was consulted. However, the lack of data for this region, makes it impossible to consider aerosol measurements provided by OMI. As an alternative, we searched the records of a station of AErosol RObotic NETwork (AERONET) located 45 km far from the city. The aerosol measurements, could be used as a first approximation into the model. 
