Dissolution of aerosol-derived iron in seawater: Leach solution chemistry, aerosol type, and colloidal iron fraction

Experiments were conducted using a semi-continuous batch protocol to leach iron from aerosol samples. In this procedure, aerosol samples were leached in an all-Teflon flow-through reaction chamber by multiple (3–4) aliquots (~ 40 mL) of leaching solution per predetermined leaching period. Several types of aerosols and leaching solutions were tested. The percent iron solubility obtained from aerosols collected in two urban regions was lower (~ 1%) than the solubility from samples collected in the open ocean (6–13%). This regional variability was greater than the variability obtained when leaching the same aerosols using different leaching solutions. A review of field and laboratory studies from the literature also suggests that different types of aerosols produce more variability in aerosol iron solubility estimates than do different leaching protocols. Colloidal iron was the dominant fraction of aerosol derived dissolved iron in all the experiments carried out during this study, suggesting that the dissolution of aerosol iron in seawater is dominated by the colloidal iron fraction.