Strong impacts of biomass burning, nitrogen fertilization, and fine particles on gas-phase hydrogen peroxide (H₂O₂)

Gas-phase hydrogen peroxide (H₂O₂) plays an important role in atmospheric chemistry as an indicator of the atmospheric oxidizing capacity. It is also a vital oxidant of sulfur dioxide (SO₂) in the aqueous phase, resulting in the formation of acid precipitation and sulfate aerosol. However, sources of H₂O₂ are not fully understood especially in polluted areas affected by human activities. In this study, we reported some high H₂O₂ cases observed during one summer and two winter campaigns conducted at a polluted rural site in the North China Plain. Our results showed that agricultural fires led to high H₂O₂ concentrations up to 9 ppb, indicating biomass burning events contributed substantially to primary H₂O₂ emission. In addition, elevated H₂O₂ and O₃ concentrations were measured after fertilization as a consequence of the enhanced atmospheric oxidizing capacity by soil HONO emission. Furthermore, H₂O₂ exhibited unexpectedly high concentration under high NO_x conditions in winter, which are closely related to multiphase reactions in particles involving organic chromophores. Our findings suggest that these special factors (biomass burning, fertilization, and ambient particles), which are not well considered in current models, are significant contributors to H₂O₂ production, thereby affecting the regional atmospheric oxidizing capacity and the global sulfate aerosol formation.