Sea-breeze circulation and photochemical pollution in Athens, Greece: Fid-Bau Portal

Sea-breeze circulation and photochemical pollution in Athens, Greece

Lalas, D.P. / Asimakopoulos, D.N. / Deligiorgi, D.G. / Helmis, C.G.

Abstract The purpose of this paper is to analyse the effect of the sea-breeze on photochemical pollution in Athens, Greece. To this end, the SO2, NO, NO2, O3 and CO concentrations, the vertical structure of the atmospheric boundary layer, the pollution emission rates and wind data are examined simultaneously for two typical days in August 1981 with well-defined sea-breeze circulation. The tendency of the complicated seabreeze flow field to stratify the atmosphere and thus generate layers with different constituents affects the concentrations measured near the ground and causes relatively high oxidant levels at night. As inversion layers descend or disappear, abrupt changes and short-period oscillations in concentrations are found, and can be explained by a simple multilayer box model. The diurnal variation and considerations based on simple ground-level wind trajectories indicate that recirculation of pollutants by the sea-breeze cell takes place, possibly aided by the small size of the basin and the closed topography. The passage of the sea-breeze front seems to have no direct effect. No day-to-day pollution accumulation is noticed. Thus, it becomes clear that if modeling of photochemical pollution in such coastal regions with pronounced relief is to be successful, it needs to pay close attention to both the flow field details and the vertical structure of the atmosphere, especially the ground-based inversion break-up and boundary layer collapse.