Abstract
Concentrations of NO2, O-3, SO2, O (x) , benzene and toluene are measured and discussed by means of a system of Differential Optical Absorption Spectroscopy (DOAS) installed at about 5m above the ground level at Tunis urban site --capital city of Tunisia ( N, 11' E). The results show that the benzene and toluene concentrations are consistent and well structured with an emphasis on the same origin sources mostly from vehicular emissions with a toluene/benzene ratio of 2.5. The winter period is characterized by high SO2 and NO2 concentrations (160 and 180 mu g/m(3), respectively). Both pollutants are influenced by the primary urban emissions mainly from heating and automobile traffic. SO2 and NO2 concentrations are also influenced by the less favorable vertical dispersion conditions characterizing the cold period of the year. In summer, ozone concentrations are higher than in winter due to the higher photochemical activity and the mixing process during this period. The warm season is characterized by higher O-3 and O (x) afternoon concentration values (up to 140 mu g/m(3)).