Highly oxygenated organic molecules are a key component of atmospheric secondary organic aerosol. The origin and formation mechanism of highly oxygenated organic molecules with high unsaturation (HU-HOMs) commonly observed in the atmosphere, however, remain unknown. Through molecular-level investigations of the photochemical aging of soot by O₂ in the air, we find that the multigenerational photo-oxidation of large polycyclic aromatic hydrocarbons (PAHs) on soot by singlet oxygen (¹O₂) and superoxide anion radicals (O₂^⋅−) can be an important source of the unexplained HU-HOMs. The PAH-derived HU-HOMs exhibit lactone and anhydride functional groups and can substantially increase the hydrophilicity of soot. As PAHs are a characteristic and ubiquitous component of combustion aerosols, their photochemical oxidation can generate substantial amounts of HU-HOMs, influencing the atmospheric fate and effects of combustion aerosols.

高氧有机分子是大气二次有机气溶胶的关键成分。然而，在大气中普遍观察到的高不饱和度高氧有机分子（HU-HOMs）的起源和形成机制仍然未知。通过对空气中O ₂对烟尘的光化学老化的分子水平研究，我们发现单线态氧（¹ O ₂）和超氧阴离子自由基（O ₂ ^⋅−) 可能是无法解释的 HU-HOM 的重要来源。PAH 衍生的 HU-HOM 具有内酯和酸酐官能团，可以显着提高烟灰的亲水性。由于 PAHs 是燃烧气溶胶的特征和普遍存在的成分，它们的光化学氧化会产生大量的 HU-HOM，影响燃烧气溶胶的大气归宿和影响。