Transport and mixing zone of desert dust and sulphate over Tropical Africa and the Atlantic Ocean region

Abstract. The potentiality of dust particles to mix with sulphate over Tropical Africa and the Atlantic Ocean is investigated by combining a meso-scale meteorological model with a dust production model and an SO₂ emission database. This mixing process study is based on a qualitative approach where the reactivity of dust is estimated from its calcite content, which is the main mineral known to be reactive with sulphur species. We are presenting a 1-month simulation (January 1993). Our results show that the regions Northern Egypt and Libya (NEL), Western Sahara (WS) and Sahel (S) are the major sources of dust plumes. The simulated dust loading is in agreement with the measured data close to the African coasts. The Mediterranean and Maghreb regions are highly influenced by European sources of sulphate, for which the simulated concentrations are consistent with the observed trends. This simplified study identifies two zones that favour the mixing process between dust and sulphate: 1. the Eastern Mediterranean basin due to the concomitance of high concentrations of dust and sulphate and 2. the North-Eastern Atlantic Ocean due to the high amount of calcite in the ejected dust which is very reactive. Thus, we assume that the coating process takes place mainly in these regions and the sulphate-coated dust found on the other side of the Atlantic Ocean (Caribbean and American coasts) is principally due to this phenomenon.