近日，广东工业大学环境健康与污染控制研究院、环境科学与工程学院安太成教授团队在小分子α-二羰基化合物的液相化学反应对棕色碳的贡献机制上取得最新研究进展。研究成果以“Oligomerization Mechanism of Methylglyoxal Regulated by the Methyl Groups in Reduced Nitrogen Species: Implications for Brown Carbon Formation”为题发表在期刊Environmental Science & Technology上。论文的第一作者为博士生石秋菊和硕士生高蕾，通讯作者为姬越蒙教授。本研究结合理论与实验手段系统探究了典型小分子α-二羰基化合物甲基乙二醛（MG）与还原性含氮化合物（RNSs）[甲胺（MA）、二甲胺（DA）和氨气（AM）]的液相反应机理，明晰了MG + MA、MG + DA和MG + AM三种目标反应体系的液相化学反应机理和动力学，揭示了RNSs中的甲基基团数量对MG的低聚反应机理及其对棕色碳形成的调控作用，阐明了RNSs中的甲基基团数量对含氮杂环产物光吸收性及潜在人体健康的不利影响，为将上述机制纳入大气模型以评估气溶胶对空气质量和人体健康的影响提供基本的动力学和机理数据。

论文网址: https://pubs.acs.org/doi/10.1021/acs.est.3c05983

棕色碳（BrC）形成机制的不明晰会影响当前气候预测中气溶胶辐射效应的驱动因素。在这里，本研究采用理论计算和实验模拟相结合的手段，系统研究了甲基乙二醛（MG）和典型还原性含氮化合物（RNSs）的液相反应机理。结果表明，在酸性条件下甲胺（MA）和氨气（AM）与MG的混合物中证实了亚胺和二亚胺生成，而在二甲胺（DA）与MG的混合物中亚胺和二亚胺不能生成，因为DA阳离子中间体的氨基被甲基基团占据，其脱质子化会受到抑制。因此，在MG + MA（MGM）和MG + AM（MGA）反应体系中会形成含氮杂环（NHC），而在MG + DA（MGD）反应体系中形成含氮链状低聚物。不同产物的形成归因于静电吸引和空间位阻，而这两种作用均受RNSs中甲基基团数量调控。此外，NHC的光吸收性及对人体健康的不利影响也与RNSs中的甲基基团数量密切相关。我们的研究结果表明BrC形成主要源于MG与具较少甲基基团数量的RNSs间的反应，这些RNSs在城市环境中含量更高且来源更广。

图文摘要：

英文摘要：

Uncertain chemical mechanisms leading to brown carbon (BrC) formation affect the drivers of the radiative effects of aerosols in current climate predictions. Herein, the aqueous-phase reactions of methylglyoxal (MG) and typical reduced nitrogen species (RNSs) are systematically investigated by using combined quantum chemical calculations and laboratory experiments. Imines and diimines are identified from the mixtures of methylamine (MA) and ammonia (AM) with MG, but not from dimethylamine (DA) with the MG mixture under acidic conditions, because deprotonation of DA cationic intermediates is hindered by the amino groups occupied by two methyl groups. It leads to N-heterocycle (NHC) formation in the MG + MA (MGM) and MG + AM (MGA) reaction systems but to N-containing chain oligomer formation in the MG + DA (MGD) reaction system. Distinct product formation is attributed to electrostatic attraction and steric hindrance, which are regulated by the methyl groups of RNSs. The light absorption and adverse effects of NHCs are also strongly related to the methyl groups of RNSs. Our finding reveals that BrC formation is mainly contributed from MG reaction with RNSs with less methyl groups, which have more abundant and broad sources in the urban environments.