Photochemical formation and transport of ozone in Athens, Greece

Abstract

An evaluation of the diurnal variation of the hourly ozone concentrations measured at five sites in Greater Athens from June until early September 1984 indicates that photosmog episodes in Greater Athens are associated with the sea breeze circulation. Due to local air circulation in the Athens basin, precursors of O 3 are transported to and accumulated in the Saronikos Bay during the morning hours while the land breeze is blowing. At noon, when the sea breeze sets in, the O 3 formed over the sea is brought back to the coast and to central Athens where it increases the local O 3 concentration by a factor of 3–5 within a few hours. The O 3 levels often remain high throughout the night. During the photochemical smog episodes, all of them accompanied by well-developed sea breezes, the U.S. Air Quality Standard of 120 ppb O 3 was exceeded for 4–7 h day −1. Peak O 3 concentrations up to nearly 200 ppb were recorded in the smog episodes. Relatively high O 3 concentrations were measured on the island of Aegina. They tend to remain high during the night and can be attributed only to primary pollutant transport from Greater Athens advected by the land breeze. The O 3 values obtained at Mount Immitos (1000 m above MSL) suggest that, first, the sea breeze inhibits the influence of vertical thermal convection up to heights above 600 m, and second, no O 3 is noticeable from above the tropopause to ground level or from long-range transport.