Interrelations of UV-global/global/diffuse solar irradiance components and UV-global attenuation on air pollution episode days in Athens, Greece

An investigation of global ultraviolet (GUV), global (G) and diffuse (Gd) solar intensities, continuously recorded over a period of five years at a station in Athens, Greece, and stored on the basis of hourly time intervals since 1996, has revealed the following: (a) UV-global irradiation, associated with the 290–395 nm wavelength region, constitutes 4.1% of global solar. (b) UV-global irradiance ranges from an average minimum of 2.4 W m−2 and 3.1% of global solar in January to an average maximum of 45 W m−2 and 7.8%, respectively, in June, both considered at 13:00, solar time. (c) There exists a good correlation among the two dimensionless irradiance ratios GUV/Gd and Gd/G in the form of an exponential relationship. (d) UV-global monthly irradiation data show evidence of temporal variability in Athens, from 1996 to 2000. (e) Anthropogenic and photochemical atmospheric pollutant agents (O3, CO, SO2, NOx, smoke) causing air pollution episodes seem to affect differently solar irradiance components. The main results of analysis (measurements within ±2 h from solar noon) indicate that a buildup of O3 and NOx inside the urban Athens plume during cloudless and windless warm days could cause: (i) UV-global irradiance depletion between 5.4% and 14.4%. (ii) Diffuse solar irradiance enhancement up to 38.1%. (iii) Global solar irradiance attenuation ranging up to 6.3%.