Resumen
The descriptive study related to the evolution of O3, NO, NO2, CO, SO2, CH4, NMHC and PM10 concentrations in downtown Sfax showed, during the period October 1996-June 1997, that the city is significantly influenced by many sources and meteorological factors. The diurnal average concentrations of these species let appear at times some peculiarities due to the population local customs and also to particular meteorological conditions associated with predominant strong cyclonic situations (cut-off lows). Based on NO and CH4, two species selected respectively as local and synoptic tracers, this descriptive study which is refined by a principal component analysis showed, out from these particular meteorological conditions, three components of the atmospheric pollution: a first component formed by CH4 and in less degree NMHC showing the impact of synoptic sources, a second component containing NO, NO2, CO, SO2 and in less degree PM10 and NMHC displaying the impact of local sources (vehicle and industrial sources), and finally a third component constituted by O3 and in less degree PM10 presenting the impact of regional sources. Under the above quoted cyclonic situations, the distribution of such components was shown considerably modified.