GAW Report No. 205 - IGAC Project

CHAPTER 6 - EUROPEprecipitation samples. In general the Istanbul rainwater pH was about 6-7, only 18.6% of the eventsshowed acidic pH below 5.6.There have also been a limited number of modelling studies that investigate the elevatedPM 10 levels in the area. The results showed that local anthropogenic emissions under unfavourablemeteorological conditions can be responsible for up to 90 per cent of PM 10 levels [Im et al., 2010].Long range transport from Europe can contribute up to 50 per cent to these high concentrations[Kindap et al., 2006].6.7.2.4 Climate effects including Heat islandKaraca et al. [1995] and Ezber et al. [1997] have studied the climatic effects of urbanizationin Istanbul. Karaca et al. [1995] statistically analyzed long-term temperature data (1912- 1992) fromstations within and around the Istanbul and reported a warming trend in urban temperatures insouthern Istanbul, which was the most densely populated part of the city, whereas in northern GIA acooling trend was observed. Ezber et al. [2007] have focused the analysis for the period from 1951to 2004 by using both statistical and numerical mesoscale modelling tools. They have shown thatthe urbanization effect on climate was most pronounced during the summer. Changes in the trendsoccurred in the 1970s and 1980s when the population growth rate in Istanbul increased dramatically.A significant expansion of the urban heat island in Istanbul has been computed for the period from1951 to 2004, fairly consistent with the expansion of the city during this period. The maximumreference-level temperature difference between the past and present simulations was found to bearound 1 o C. The modelling experiment by Ezber et al. [2007] also indicated that the velocity of theprevailing northeasterly wind and the water vapour mixing ratio were both reduced over the city.6.7.3 The Greater Athens Area6.7.3.1 City characteristics, geography, population, meteorologyGreece has one of the most aged populations in Europe with almost one fifth over 65 yearsold. In 2004 the annual deaths of 104 000 inhabitants were slightly higher than the 101 000 births. In2004, the life expectancy of the total population at birth was 79 years. The male population, whichconstitutes 50% of the national total population, has a lower life expectancy (77 years) than females(82 years), one of the highest in Europe [WHO, 2006]. The Greater Athens Area (GAA) currentlyhas a population exceeding 4 million inhabitants, which is about 40% of the total population ofGreece, and has experienced a population growth rate of 0.6% per year over the last decade.The climate of Athens is typically Mediterranean with hot dry summers and wet mild winters.The mean daily summer and winter temperatures are 25.8 o C and 10.1 o C, respectively. The meanannual total precipitation is about 400 mm, 85% of which occurs from October to March [Kalabokaset al., 1999a]. The mean wind pattern in the atmospheric boundary layer in Athens during thewarmer part of the year is a persistent northeasterly flow. The Athens basin is exposed to thesummer monsoon circulation of the Eastern Mediterranean. The city of Athens is located in a basinon the west coast of the Attica peninsula (Figure 37). It is surrounded by moderately high mountainsforming a channel with only one major opening toward the sea to the southwest. The mountains actas physical barriers with only small gaps between them. The most important gap is the channelbetween Hymmetus and Pendeli leading to the northeast coast of the Attica peninsula that gives theAthens basin access to the Etesians, a system of semi persistent northerly winds. During theappearance of the Etesians, good ventilation of the basin is favoured and thus pollution episodes donot appear. The weakening of the synoptic wind allows the development of local circulation systems,such as sea/land breezes along the axis of the basin (NE to SW) and anabatic/catabatic flows fromthe surrounding mountains. During such cases, the ventilation of the basin is poor, the boundarylayer is shallow, and the air pollution potential increases [Melas et al., 1995 and references therein].Air pollution episodes may occur in Athens during all seasons of the year but most of theseepisodes are associated with the development of sea-breeze [Kallos et al., 1993].238