North African soil dust and European pollution transport to America during the warm season: Hidden links shown by a passive tracer simulation

Authors: G. Gongoiti, L.Alonso, M. Navazo, J.A. García, M. Millán - ENGLISH - 2006 - 25 pgs.

Abstract: A mesoscale atmospheric model coupled with a dispersion model is used to establish source-receptor relationships between the European-North African aerosol episodes observed over the Caribbean every year during summer and their main sources. The simulation period extends from 15 July to 16 August 1991, concurrent with the flight campaign of the European Project RECAPMA (Milla´n et al., 1997; Gangoiti et al., 2001). We now extend the simulations to reach the tropical Atlantic and the Caribbean, and we make use of the TOMS aerosol index data (Nimbus 7 satellite) to substantiate the simulations at the regional-to-continental scale. Our simulations, based on passive tracer release from selected source regions, show that emissions from southern Europe can either take a full-Atlantic shortcut to the American coasts or enter the Mediterranean basin eastward to turn back to America following a longer pathway: The emissions cross the southern Mediterranean coast to northern Africa, and then they are vented to the middle troposphere (2000–6000 m MSL), mixed within the Saharan air layer (SAL) and transported westward to the tropical Atlantic (TA) and America. Recirculations around the Atlas Mountains and perturbed conditions over the area modulate the export of the European tracer (and soil dust) into America. We found transit times of 11–12 days for the full Atlantic shortcut and 20–26 days for the longer pathway across northern Africa. Under the simulated conditions, southern Europe can contribute with more than the 50% of its emissions to America, while northern Europe shows longer transit times and less transport efficiency.