Abstract：
Hydrogen peroxide (H2O2) plays a crucial role as an oxidizing agent within the tropospheric environment, making a substantial contribution to sulfate formation in hydrated aerosols and cloud and fog droplets. Field observations show that high levels of H2O2 are often observed in heavy haze events and polluted air. However, the source of H2O2 remains unclear. Here, using the droplets formed in situ by the deliquescence of hygroscopic compounds under a high relative humidity (RH), the formation of H2O2 by the photochemistry of imidazole-2-carbaldehyde (2-IC) under ultraviolet irradiation was explored. The results indicate that 2-IC produces IM-C•-OH and IM-C•═O radicals via H transfer itself to its excited triplet state and generates H2O2 and organic peroxides in the presence of O2, which has an evident oxidizing effect on SO2, suggesting the potential involvement of this pathway in the formation of atmospheric sulfate. H2O2 formation is limited in acidic droplets or droplets containing ammonium ions, and no H2O2 is detected in droplets containing nitrate, whereas droplets containing citric acid have an obvious promotion effect on H2O2 formation. These findings provide valuable insights into the behaviors of atmospheric photosensitizers, the source of H2O2, and the formation of sulfate in atmospheric droplets.
摘要：
过氧化氢（H2O2）作为对流层环境中的氧化剂起着至关重要的作用，对水合气溶胶以及云滴和雾滴中的硫酸盐形成做出了重大贡献。现场观察表明，在严重的雾霾事件和污染空气中经常观察到高水平的H2O2。然而,H2O2的来源尚不清楚。这里,使用在高相对湿度（RH）下通过吸湿性化合物的潮解原位形成的液滴，探索了在紫外线照射下咪唑-2-甲醛（2-IC）的光化学作用下H2O2的形成。结果表明，2-IC产生IM-C•-OH和IM-C•=O自由基通过H转移到其激发的三重态，并在O2存在下产生H2O2和有机过氧化物，这对SO2具有明显的氧化作用，表明该途径可能参与大气硫酸盐的形成。H2O2的形成限制在酸性液滴或含有铵离子的液滴中，在含有硝酸盐的液滴中没有检测到H2O2，而含柠檬酸的液滴对H2O2的生成有明显的促进作用。这些发现为大气光敏剂的行为提供了有价值的见解，H2O2的来源，并在大气液滴中形成硫酸盐。
