Time-dependent release of iron from soot particles by acid extraction and the reduction of fe3+ by elemental carbon

Elemental carbon reduces Fe3+ to Fe2+ in aqueous solutions. This process has potential implications in the adverse health effects of fine particles in air pollution, because both elemental carbon and iron are major components in atmospheric particulate matter. In this study we measured the time-dependent release of iron from laboratory flames and standard reference soot particles that contained iron, and the reduction of Fe3+ to Fe2+ in an acid extraction process. The concentration of Fe3+ and Fe2+ ions in the extraction solutions was measured by a spectrophotometric method. The results showed that while Fe3+ was the dominant valence state in the dry soot particles, significant fraction of iron was reduced to Fe2+ in the aqueous solution. Further investigation is needed to assess the significance of this phenomenon in the biological effects of particles that contain iron and elemental carbon.