Soluble Fe in Aerosols Sustained by Gaseous HO2 Uptake

Abstract

The soluble fraction of aerosol Fe, mainly Fe(II), represents a large source of nutrient iron to the open ocean. Fe(II) may also play an important role in the adverse health effects of ambient aerosols. Our current understanding of the reduction of Fe(III) to Fe(II) in aerosols suggests that the major pathway is the photoreduction of Fe(III)–oxalate complexes, but this pathway cannot explain the observed nighttime Fe(II) in ambient aerosols and is also limited by the supply of oxalate. Here we propose a new pathway initiated by gaseous HO2 uptake, followed by Cu–Fe redox coupling, which can sustain nighttime Fe(II) and also dominate Fe(III) reduction in the absence of Fe(III)–oxalate complexes. Consequently, aqueous OH production is substantially enhanced via the Fenton reaction and sustained by the influx of HO2 from the gas phase. This mechanism is potentially the major mechanism for sustaining soluble Fe(II) in ambient aerosols and can be tested by a combination of modeling and aerosol Fe speciation me...