Tracking the changes of iron solubility and air pollutants traces as African dust transits the Atlantic in the Saharan dust outbreaks

Abstract

We studied the solubility, in real sea water, of iron present in the African dust outbreaks that traverse the Atlantic. Based on measurements of soluble iron (sFe) and aerosol chemistry, we found iron solubilities within the range of 0.4–1.8% in Tenerife, 0.4–3.1% in Barbados and 1.6–12% in Miami. We apportioned the concentrations of sFe between the three sources and processes that we identified: (1) dust, (2) heavy fuel oil combustion emissions, associated with an excess of vanadium and nickel, and (3) atmospheric processing, which is influenced by acidic pollutants. We tracked the propagation of the dust-front of the African dust outbreaks across the Atlantic, which are associated with dust peak events at the impacting sites. During the westward transport across the Atlantic, the contribution to sFe from dust decreased (63%, 42% and 11% in Tenerife, Barbados and Miami, respectively), whereas the contribution due to atmospheric processing increased (26%, 44% and 80% in Tenerife, Barbados and Miami, respectively). In these Saharan-dust outbreaks, the concentrations of sFe due to heavy fuel oil combustion were significantly lower (mostly < 5 ng/m3) than those in the polluted marine atmosphere (10–200 ng/m3). The overall results are consistent with the idea that the mixing of dust with acid pollutants increases the solubility of iron during the African-dust outbreaks that traverse the Atlantic.