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 SO 2 oxidation is a dominant sulfate source. We demonstrate that black carbon (BC) critically enhances this process through interfacial electronic interactions with HSO 3 − /SO 3 2− species, reducing SO 2 oxidation barriers while increasing reactive oxygen species (ROS) generation ( 1 O 2 , •O 2 − , and •OH). Unique sulfur isotopic signatures measured in BC-Mn 2+ /O 2 systems confirm a novel oxidation pathway in which BC facilitates electron transfer during O 2 -activated SO 2 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 O 2 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.