We examine iron in atmospheric fine aerosol particles collected over the Indian Ocean during shipborne observations in November 2018. Transmission electron microscopy analysis with water dialysis shows that various types of iron (fly ash, iron oxide, and mineral dust) co-exist with ammonium sulfate and that their solubility differs depending on the iron type. Using PM_2.5 bulk samples and global model simulations, we elucidate their origins, aging, and implications for present iron simulations.