Insights into black carbon-activated manganese catalysis in atmospheric sulfate production

The mechanisms that produce atmospheric sulfate, a critical PM_2.5 constituent, must be elucidated to inform air quality interventions. Current evidence indicates that manganese-catalyzed heterogeneous SO₂ oxidation is a dominant sulfate source. We demonstrate that black carbon (BC) critically enhances this process through interfacial electronic interactions with HSO₃^-/SO₃^2- species, reducing SO₂ oxidation barriers while increasing reactive oxygen species (ROS) generation (¹O₂, ·O₂^-, and ·OH). Unique sulfur isotopic signatures measured in BC-Mn²⁺/O₂ systems confirm a novel oxidation pathway in which BC facilitates electron transfer during O₂-activated SO₂ conversion. Multiphase modeling revealed that under typical haze conditions, BC-mediated catalysis produces sulfate at higher rates than traditional Mn-only pathways. The synergistic BC-Mn system enables continuous redox cycling via O₂ activation, establishing BC as an active electronic modulator rather than a passive substrate in sulfate formation. These findings redefine the role of BC in atmospheric chemistry, offering a molecular basis for targeted sulfate aerosol control.