Atmospheric iron supply is important for ocean biogeochemistry and iron solubility in aerosol is a key uncertainty in our understanding of that atmospheric supply.It is widely reported that the percentage of soluble iron in mineral aerosol is higher than in the parent soil from which the aerosol is derived.It has been suggested that this effect is caused by reactions of acids on the mineral surface during transport through the atmosphere and several laboratory studies have shown that iron release from aerosols is inversely related to pH.However,attempts to verify that this effect is important in the atmosphere – by relating field measurements of aerosol iron solubility to measured acid species concentrations – have proved inconclusive.We recently proposed that the dominant influence on aerosol iron solubility during large-scale atmospheric transport is physical rather than chemical: Larger mineral particles are removed preferentially during transport because of higher settling rates.This leads to a progressive shift to smaller mineral aerosol population size spectra,with correspondingly larger surface area to volume ratios.Thus the percentage of total iron close to the surface of mineral particles,and available for dissolution,also increases.Here we will explore various aspects of chemical and physical processing of mineral aerosol during transport and show,among other things,that looking for relationships in field data between aerosol iron solubility and acid concentrations is likely to be a futile exercise.