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 H(2)O(2 )concentrations up to 9 ppb, indicating biomass burning events contributed substantially to primary H2O2 emission. In addition, elevated H2O2 and O-3 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 NOx 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