On the trend of the transmittance of direct solar irradiance in Athens during the summer

In recent years, high concentrations of air pollutants in Athens have been measured. Since 1962 measurements of the broadband direct solar irradiance, which is directly affected by the aerosol loading in the atmosphere, have been avialable from the National Observatory of Athens (NOA). Using these data, the year to year trend of the mean value of the midday transmittance with clear sky in summer is evaluated for the period 1962–1985. A pronounced decrease of the transmittance occurred between the years 1962 and 1975. This probably reflects the rapid urbanization of the Athens area.