Iron solubility in mineral dust and aerosols generated from soil samples

Abstract

Studies of Fe solubility are vital to improve knowledge of Fe speciation in the mineral aerosols and its bioavailability to marine organisms. During atmospheric transport, mineral aerosol particles undergo various processes that may increase its solubility. Most important are changes in pH, which occur during cloud formation. In this work we have simulated the cycle of condensation and evaporation of clouds in samples of sieved African soils samples and compared the Fe solubility with natural mineral aerosols dry deposition (DD) samples collected on the island of Gran Canaria. The percentage of soluble Fe in the “precursor” aerosol increased from 0.19% to 0.67%, which was in agreement with values for the DD samples (0.23-0.68%). Our results show the effectiveness of the cloud simulation process, since there was a fivefold increase in the solubility of Fe, resulting in aerosol solubility comparable to that found in natural aerosol samples. Comparing the Fe speciation in soil and aerosol precursor samples with aerosol samples collected in Gran Canaria, a connection between chemical properties of aerosols and their soil origins can be demonstrated. Moreover, the high variability in Fe speciation in dry deposition samples suggests that atmospheric transport may be an important factor controlling aerosol solubility.