Measurements of Rural Surface Ozone at a Remote Island Site in the NE Aegean Sea: Indications of Regional / Transboundary Transport

Abstract

Relatively high levels of rural surface ozone concentrations, with increasing trends, have been observed in several parts of the world, particularly in the Northern Hemisphere. While in Central and Northern Europe many rural air pollution stations are operating, providing a satisfactory picture of the spatial distribution of ozone concentrations, only a limited number of systematic measurements exist for the Mediterranean Basin. In the present study, results of rural surface ozone data collected in the air pollution station, which was operated at a remote island site in the North - East Aegean Sea, on NE Lesvos Island, are presented for the period of June 2001 till October 2001. The position of the station, without any major local emission sources in a distance less than 200 km, permits the detection of the rural ozone levels. Measurements of nitrogen oxides and SO₂ were conducted at the same time. The data set comprises hourly values of O₃ concentrations taken with a UV photometric analyzer, SO₂ concentrations with a UV fluorescence analyzer as well as NO/NO₂ concentrations with a chemiluminescence analyzer. The results showed very low values for SO₂ and NOx, however, the O₃ concentrations were considerably higher than those expected at unpolluted areas; the 8- hours running average frequently exceeds 60 ppb. During the same period and for some nighttime episodes, the history of air masses arriving at the measuring station is studied by calculating back trajectories, aiming to study the origin of the incoming air masses. The high persistence of the Etesians winds, - a circulation system consisting of a northerly wind flow, unique to the eastern Mediterranean during the warm period of the year - might provide the means for regional / transboundary transport of air pollutants in the area.