OZONE DYNAMICS OVER GREECE AS DERIVED FROM SATELLITE AND IN-SITU MEASUREMENTS

A comprehensive analysis of the records of surface ozone available for Athens, Greece (38 degrees N, 24 degrees E) for the periods 1901-1940 and 1987-1990 is presented. Both records are analysed to explore the intraseasonal fluctuations and the harmonic components of surface ozon e and also compared to other historical surface ozone records. The var iation in surface ozone concentration during rainfall is also investig ated, using the hourly measurements of the surface ozone concentration obtained by a network of four stations within the Greater Athens area . The results indicate that, during rainfall events which are associat ed with the passing of a cold front, an important decrease of the surf ace ozone concentration is observed. Daily measurements of surface ozo ne and NOx from five stations in the Greater Athens Basin over the per iod 1986-1990 are also used in order to examine the main features of b asin-wide O-3-HC-NOx relations. A simple regression model between the surface ozone concentration and the temperature at the 850 hPa level, which was first tested in Los Angeles, gave satisfactory results in re producing the mean monthly ozone variation in Athens, when coefficient s extracted from local data were used in the regression equation. A se ries of vertical ozone soundings over Athens has been also performed i n order to explore the tropospheric ozone variations and to examine fu rther the transport that occurs at the 700 hPa level with advection fr om the north-western sector. The relevant results are discussed. The e xisting uncertainties concerning the stratosphere-troposphere exchange of ozone which mainly occurs during mid-latitude tropopause folding a s well as during cut-off low events are also discussed. The examinatio n of the role of the atmospheric circulation in the lower stratosphere in relation to the laminated structure of ozone is also attempted. Th e data collected during the balloon ascents have been compared with th ose during the balloon descents. Both profiles are compared with the t otal ozone measurements derived from the TOMS on the Nimbus-7 satellit e and the Dobson spectrophotometer. The data collected for the vertica l distribution of ozone and temperature have been compared with the sa tellite-derived reference models which provide the monthly latitudinal variations of vertical structure of both ozone and temperature. We ha ve also used total ozone measurements obtained with a Dobson spectroph otometer (No. 118) which has been instituted in Athens from 1989 in or der to examine the consistency of data from TOMS with the correspondin g Dobson data on a daily basis. Furthermore monthly mean total ozone d ata were first estimated for the entire period and were then Fourier a nalysed to obtain the amplitude, phase and percentage,contribution to the total variance of the first, second and third harmonics.