Emerging nitrogen-driven urban atmosphere control on aerosol iron dissolution for biogeochemical cycles.

Iron (Fe) is a critical micronutrient regulating marine productivity and the global carbon cycle, yet its atmospheric dissolution mechanisms remain debated for biogeochemical cycle. The prevailing "iron-sulfur coupling" paradigm has traditionally explained proton-promoted dissolution. However, disproportionate declines in sulfur dioxide relative to nitrogen oxides emissions have created a "low-sulfur, high-nitrogen" atmosphere over East Asia, raising questions about the role of nitric acid. Here, we develop a data-driven framework to elucidate nitric acid-driven Fe dissolution using the nitrate-to-sulfate acidification capacity ratio (RN/S). Results show that nitrate now dominates urban aerosol Fe dissolution, contributing ∼1.5 times more than sulfate, challenging the long-standing paradigm. Global simulations further estimate that nitrate contributes to ∼68% of the enhancement in Fe solubility in PM2.5 (particulate matter with a diameter of 2.5 μm) dust relative to preindustrial levels. These findings reveal an emerging nitrogen-driven control on Fe mobilization, emphasizing the need to incorporate species-dependent acid chemistry into models to accurately represent global Fe cycling and its climate feedbacks.