The general climatic conditions and the physiographic characteristics of the area around the Mediterranean Sea, result in the formation of a flow pattern which is from North to South during all seasons and mainly during summer. This flow transports polluted air masses from southern Europe towards Africa. This transport is being investigated with the combined use of an atmospheric and a Lagrangian dispersion model. Air pollutants released from sources located in southern Europe were found in the entire tropospheric region over North Africa. The time scales for such a transport were found to be four to six days. This kind of transport can have several implications ranging from degradation of the air quality in North African cities to the water budget and regional climatic change. ¿ 1998 American Geophysical Union