Mechanistic insights into I 2 O 5 heterogeneous hydrolysis and its role in iodine aerosol growth in pristine and polluted atmospheres

Higher-order iodine oxides are intricately linked to marine aerosol formation; however, the underlying physicochemical mechanisms remain poorly constrained, particularly for I 2 O 5 , which is stable yet conspicuously absent in the atmosphere. While reactivity with water has been implicated, the direct hydrolysis of I 2 O 5 (I 2 O 5 + H 2 O → 2HIO 3 ) fails to account for this discrepancy due to its high activation barrier (21.8 kcal mol −1 ). Herein, we have probed heterogeneous hydrolysis of I 2 O 5 mediated by prevalent chemicals over oceans through Born-Oppenheimer molecular dynamics and well-tempered metadynamics simulations. Our results demonstrate that self-catalyzed pathways involving I 2 O 5 and its hydrolysis product HIO 3 substantially reduce the reaction barrier, thereby accelerating the conversion of I 2 O 5 to HIO 3 in pristine marine environments. In polluted regions, interfacial hydrolysis of I 2 O 5 mediated by acidic or basic pollutants (e.g., H 2 SO 4 or amines) proceeds with even greater efficiency, characterized by remarkably low barriers (≤ 1.3 kcal mol −1 ). Collectively, these proposed heterogeneous reactions of I 2 O 5 are relatively effective, acting as a hitherto unrecognized sink for I 2 O 5 and a source of HIO 3 – processes that facilitate marine aerosol growth and rationalize the high iodate abundances detected in aerosols. These findings provide mechanistic insight into the elusive I 2 O 5 -to-HIO 3 conversion, offering an unheeded step toward improving the representation of iodine chemistry and marine aerosol formation in atmospheric models, with implications for climate prediction and environmental impact assessment.