Air Quality Monitoring in the Mediterranean Tunisian Coasts

Abstract

The transfer from the liquid element (the sea) to the solid one (the land) engenderers thermal phenomena such breezes. During the day, the land heats up more rapidly than the sea. Over the land surface, the heat spreads in the low layers and gives birth to upward currents. This hot continental air rises up, and then is superseded by a colder air coming from the sea; it is the sea breeze. During the night, the phenomenon is reversed to become a land breeze. If the synoptic wind is weak, the breezes will take their true size and result in the formation of convergent zones on the land and divergent zones over the sea. Some visual signs can help observe these phenomena. The low clouds of the cumulus type are a proof of the vertical movement. They are often related to the setting of the sea breeze (Simpson, 1994). Many experimental and numerical studies have shown the impact of breeze circulations on the evolution of pollutant concentrations (Bouchlaghem et al., 2007; Srinivas et al., 2007; Baumgardner et al., 2006; Evtyugina et al., 2006; Flocas et al., 2006; Lim et al., 2006). The photochemical transformation also plays a crucial role in the production and destruction of pollutants. These transformations coupled with the dynamic circulations such as breezes represent the responsible process of the formation, transport and redistribution of reactive chemical species in the low layers of the atmosphere. The study made by (Ma and Lyons, 2003) via a 3D version of RAMS model (Regional Atmospheric Modelling System) has shown that the recirculation of pollution is a Mediterranean characteristic. They have defined the recirculation as follows: in the presence of a weak synoptic wind, the heating and cooling of the land and the sea determine the local circulation which affects the transport and diffusion of emissions. In fact, during the night, emissions can be transported over the sea via a land breeze or an offshore synoptic wind just to return onshore to the land after the launching of the sea breeze. The study of (Nester, 1995) has shown that the phenomena of photochemical Smog are generally associated with this type of meteorological conditions such as, a weak synoptic wind and a recirculation of 11