Long-term ozone and UV variations at Thessaloniki, Greece

Abstract

Total columnar ozone has been decreasing over middle latitudes (20°–60°) between 1979 and December 2000 at rates of about 4% in winter/spring and about 2% per decade in the summer. Total ozone trends through 1997 and through 2000 differ only over the middle and high latitudes of the northern hemisphere. This long-term trend was interrupted by periods of enhanced volcanic activity, which resulted to significant ozone losses (more than 5% per year) following large volcanic eruptions (El Chichon in 1982 and particularly Mt Pinatubo in 1991). Linked to the ozone decrease are well-documented global increases of the harmful UV-B solar radiation levels reaching ground level. Through 1997 the erythemal dose over middle latitudes in clear skies was increasing at rates exceeding 5% per decade while the solar UV irradiance at the lower wavelengths was increasing by more than 10% per decade, partly enhanced by the decrease of air pollutants such as sulfur dioxide in the case of Thessaloniki. However, evidence is presented in this study that during the last decade (1990–2001) over Thessaloniki, the ozone trend was smaller the order of −1.5% per decade. Also the associated increasing trends in the erythemal dose and at 305 nm are smaller not exceeding +2% and +4% per decade respectively under clear skies. The long-term UV variability has a QBO component, which cannot be overlooked, even in comparison with the amplitude of the annual cycle.