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 (G(UV)), global (G) and diffuse (G(d)) 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 G(UV)/G(d) and G(d)/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 (O-3, 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 O-3 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%. (C) 2002 Elsevier Science Ltd. All rights reserved.