Chemical characterisation of iron in dust and biomass burning aerosols during AMMA-SOP0/DABEX: implication for iron solubility

摘要

The chemical composition and the soluble fraction were determined in aerosolsamples collected during flights of AMMA-SOP0/DABEX campaign, which wereconducted in the West African Sahel during dry season (2006). Two aerosoltypes are encountered in this period: dust particles (DUST) and biomassburning aerosol (BB). Chemical analysis and microscope observations showedthat the iron (Fe) found in BB samples mainly originates from dust particlesmostly internally mixed in the biomass burning layer. Chemical analyses ofsamples showed that the Fe solubility is lower in African dust samples thanin biomass burning aerosols. Our data provide a first idea of thevariability of iron dust solubility in the source region (0.1% and3.4%). We found a relationship between iron solubility/claycontent/source which partly confirms that the variability of iron solubilityin this source region is related to the character and origin of the aerosolsthemselves. In the biomass burning samples, no relationship were foundbetween Fe solubility and either the concentrations of acidic species(SO, NO or oxalate) or the content of carbon (TC,OC, BC). Therefore, we were unable to determine what processes are involvedin this increase of iron solubility. In terms of supply of soluble Fe tooceanic ecosystems on a global scale, the higher solubility observed for Fein biomass burning could imply an indirect source of Fe to marineecosystems. But these aerosols are probably not significant because theSahara is easily the dominant source of Fe to the Atlantic Ocean.