**2.2.8 Water surfaces**

424 Solar Radiation

Cement products are the most widely used materials for the open spaces of Athens, and of every other Greek city. Concrete with visible aggregates of various sizes (gravel cement), which is poured on site, is mainly used for the paving of squares, pedestrian streets and urban furniture, such as sitting areas. Slabs are used in sidewalks, while blocks are used in pedestrian and low-traffic streets. As was expected, the light-coloured materials (gravel cement and the white slabs) were cooler than the dark-coloured ones (the grey cement slabs, the red mosaic slabs, the gravel cement slabs and the grey cement blocks). It should be noted that the surface temperatures of all the materials, except of the white slabs, were 3.5 to 5.5 oC hotter than the air around sunset. Also, that the differences in the surface temperatures of

Ceramic blocks are used in the urban open spaces of Athens in very few cases, mainly in pedestrian streets. In this study, the temperature of the beige ceramic blocks were measured in Korai Pedestrian Street. Due to their colour, the materials did not exhibit very high

Wood is very seldom used in the open spaces of Greek cities. In this study, the temperature of wood surfaces was measured in three cases. Wooden surfaces showed very high surface temperatures, which were comparable even with the surface temperatures of asphalt (Table 1). The mean maximum temperature of wood was 60 oC, its mean temperature was 46.2 oC, while its surface temperature at 19:30 was 28.7 oC, and much lower than the air temperature at that time.

In the urban open spaces, asphalt products are only used in the form of asphalt concrete, which is widely used for the paving of streets. Asphalt surfaces's temperatures were measured in most urban open spaces. In most cases, their surface temperatures in the afternoon (13:30 - 16:30) were over 50 oC, in some cases, greater than 60 oC. At this point, a distinction should be made between newly and old paving. The weathering of asphalt concrete causes the appearance of its aggregates to be usually white, crushed, light-coloured stone and a subsequent increase in its reflectivity. Apart from the apparent differences in the maximum and mean temperatures, it is interesting to note the surface temperatures of the material around sunset (about 19:30). At this time, air temperatures are around 32 oC, while surface temperatures of new asphalt are 7 oC higher, and that of old asphalt are about 4.5 oC

Vegetal surfaces, such as grass and shrubs, are continuously becoming scarce in the centre of Athens, and their temperatures were measured in few open spaces. As it can be seen in Table 1, in general, vegetal surfaces remain relatively cool during the day. Only the dry grass surface had maximum and mean temperatures equal to 45 and 34.5 oC, while the evergreen shrubs

exposed and shaded materials were in all the cases significant.

**2.2.3 Cement products** 

**2.2.4 Ceramic products** 

**2.2.5 Wooden products** 

**2.2.6 Asphalt products** 

**2.2.7 Vegetal surfaces** 

higher, while of shaded asphalt are 2.5 oC lower.

surface temperatures (Table 1).

Water surfaces are encountered in the centre of Athens mainly in the form of fountains. The water surfaces, of which temperature were measured in this study were fountains in Kotzia Square and in Eleftherias Square, which showed very low surface temperatures. The obtained maximum and mean surface temperatures were 25.5 and 25.6 oC, respectively, while their surface temperature around sunset was 25.5 oC. It was noted that water surfaces, even in the case of non-functioning jet fountains, were constantly cooler than the air.



Table 1. Overview of the in-situ surface temperature measurements in urban open spaces.

#### **2.3 Results of experimental measurements of paving materials**

The results of the experimental measurements, are presented in Table 2.

Fig. 4. Experimental measurements of paving materials. Placement of samples on a flat roof surface.

Fig. 5. Experimental measurements of paving materials. Placement of samples on a flat roof surface.
