The analysis is based on hourly radiometric data collected at the urban site of the Athens University Campus (388N, 248E, 205 m above MSL), for a 2-year period (1 January 2000–31 December 2001). The experimental site is located in the eastern border of the Athens basin on the slopes of Mt. Hymettus. Global solar irradiance RS (305–2800 nm) was measured with a Kipp & Zonen model CM-3 (Delft, The Netherlands), while another Kipp & Zonen CM-3 with a polar
axis shadow band was used to measure diffuse irradiance Rd. The photosynthetic photon flux density QP (400–700 nm) was measured with a Kipp & Zonen PAR-Lite model quantum sensor (Delft) given in photo-biological units (mmol m2 s1), whereas another PAR-Lite quantum sensor with a polar axis shadow band was used to measure diffuse photosynthetic photon flux density QPd.