Effect of Black Carbon on the Gas-Phase Oxidation of SO2 by H2O2 to Form Sulfate

Abstract

A common carbonaceous aerosol in the atmosphere that absorbs light is called black carbon (BC). During haze situations, it can be crucial to the development of sulfate. In this work, we used a flow tube reactor system to replicate the gas-phase oxidation of SO₂ by H₂O₂ in the presence of BC. We looked into the fundamental process as well. According to our findings, BC greatly encourages the development of sulfates. Stronger UV light intensity, higher BC mass concentration, and higher H₂O₂ concentration all promote this amplification. The reaction exhibits pseudo-first-order kinetics, according to kinetic analysis. When BC is present, the absorption coefficient rises to 2.728 × 10^-7, indicating a significant increase in reaction rate. We identified the microscopic process by XPS analysis and radical scavenging studies. The "pre-adsorption–oxidation" route is followed in the production of sulfate. In particular, SO₂ initially adsorbs onto the surface of BC. The reaction energy barrier is subsequently lowered by electron transfer, enabling further oxidation to sulfate. Additionally, BC catalyzes the breakdown of H₂O₂ to produce singlet oxygen (¹O₂), superoxide radicals (·O₂^-), and hydroxyl radicals (·OH). The conversion of SO₂ is accelerated by these extremely reactive oxygen species. This study emphasizes how important BC is in encouraging the development of atmospheric sulfates. It offers a fresh theoretical foundation for improving our comprehension of atmospheric sulfate production processes.