How Acid Iron Dissolution in Aged Dust Particles Responds to the Buffering Capacity of Carbonate Minerals during Asian Dust Storms

Aerosol deposition significantly impacts ocean ecosystems by providing bioavailable iron (Fe). Acid uptake during the transport of Fe-containing particles has been shown to cause Fe dissolution. However, carbonate in dust particles affects the Fe acidification process, influencing Fe dissolution. Here, we carried out atmospheric observations and modeling to show that Fe solubility substantially increased from locations near dust sources to downwind regions in aged dust particles with pH > 3, driven by proton-promoted dissolution. We found that Fe solubility remained low when Ca solubility was under 45 ± 5%, but increased with Ca solubility when it was above 45 ± 5%. Moreover, we found that Fe dissolved in aqueous Ca-nitrate coatings on Fe-containing dust particles. Our results suggest that the mixing state and buffering capacity of carbonate and Fe minerals should be represented in atmospheric biogeochemical models to more accurately simulate acid Fe dissolution processes.