In this study day by day synoptic conditions are classified over the Attica peninsula for a period of sixteen years. Eight synoptic categories which are demonstrated to be statistically distinct are selected with respect to the atmospheric circulation in the lower troposphere. Furthermore, a methodology is proposed to classify the mesoscale patterns for the same period on the basis of surface wind measurements, and this distinguishes eleven distinct mesoscale categories. In general, the frequency analysis reveals that the anticyclonic circulation dominates while the weak mesoscale flows prevail, with preference in May and June. A day by day cross tabulation of the synoptic flow patterns with the mesoscale categories is then performed in order to identify the association of the synoptic conditions with the mesoscale flow regime. It was found that the synoptic conditions at the level of 850 hPa are closely related to the observed surface local flows and therefore it is suggested that the synoptic categories can be used for the identification of the most favourable mesoscale atmospheric circulation.

In this study an attempt is made to examine and analyse the mean characteristics of the katabatic flows at the western slope foot of a 1024m high knife edge mountain using a meteorological tower and three surface meteorological stations. In addition, the frequency distribution of the occurrence of the katabatic flow over one year period is studied along the characteristics of the flow arriving in the neighbouring urban area at a distance of 1.5km. It was found that the katabatic flow occurs mainly in autumn and spring with the highest frequency in April. The flow is generally characterised by small depth as it is affected substantially by the background flow. The expected direction of the katabatic wind dominates mainly at the level of 7 m, where the influence of the background flow is minimised. At the level of 18m the wind direction shifts, due to the interaction of the katabatic wind with the background flow. The katabatic flow can penetrate at a distance of 1.5 km being substantially weakened.

The daily relationship between synoptic circulation in the lower troposphere and air quality conditions is demonstrated over the Athens Metropolitan Area (AMA) for the period between 1983 and 1995. This approach utilises eight distinct synoptic categories at the isobaric level of 850 hPa and air quality indicators with respect to O3, NO2, CO, SO2 and black smoke (BS). It is demonstrated that high concentrations of photochemical pollutants and SO2 are closely related to the synoptic scale circulation while CO and BS show a weaker correlation. The most favourable synoptic pattern for the accumulation of high concentrations is the open anticyclonic circulation and for the occurrence of extreme events the closed anticyclone. NO2 and BS present the highest frequency of severe events. The seasonal analysis reveals that the bad and extreme air quality conditions due to O3 and NO2 prevail in the warm season while during the cold season CO and SO2 events prevail. The synoptic category representing a combination of high and low pressure systems, commonly associated with an intense wind flow over the Aegean Sea in the warm period, seems to favour the accumulation of photochemical pollutants, especially O3, over the AMA. The converse relationship was found for the SO2 case. During cold periods, the synoptic category characterised by ’zonal flow’ seems to favour the development of bad conditions for NO2 and particularly CO.

The objective of this study is to identify and establish the day-by-day relationship between mesoscale circulation and the air quality status over the Metropolitan area of Athens for a period of 13 years and to further investigate its temporal and spatial variability. Eleven distinct mesoscale patterns are identified using a formulated methodology based on surface wind measurements. The air quality conditions are classified into seven distinct classes according to the method of the Air Quality Indicators for five main pollutants namely, O3, NO2, SO2, CO and black smoke (BS). It was found that severe and bad air quality conditions over specific parts of the examined area are associated with the weak mesoscale patterns of southern direction or calm conditions. The good and moderate conditions are established mainly under northerly airflows. The most serious pollution problem favored even by intense northerly flow is attributed to O3 during the warm period in the northern zone. High concentrations of O3, NO2 and SO2 in the warm period are remarkably related to the pure sea breeze circulation, especially in the central and northern zone.