Reassessing the atmospheric oxidation mechanism of toluene
Reassessing the atmospheric oxidation mechanism of toluene
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重新评估甲苯的大气氧化机理
DOI：
10.1073/pnas.1705463114
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发表时间：
2017-08-01
影响因子：
11.1
通讯作者：
Zhang, Renyi
中科院分区：
文献类型：
--
作者：
Ji, Yuemeng;Zhao, Jun;Zhang, Renyi
芳香烃的光化学氧化导致对流层臭氧和二次有机气溶胶（SOA）的形成，对空气质量，人类健康和气候具有深远的影响。甲苯是城市环境中最丰富的芳香族化合物，但其详细的化学氧化机理尚不清楚。结合实验室实验和量子化学计算，我们展示了一种不同于当前大气模型中所采用的甲苯氧化机制。我们的实验工作表明甲酚的支化比大于预期，但开环产物的形成可忽略不计（例如，甲基乙二醛）。量子化学计算还表明，甲酚是更稳定的，比它们相应的过氧自由基，和，最有利的OH（邻位）加成，H提取的途径O-2形成甲酚进行的障碍比O-2加成形成过氧自由基。我们的研究结果表明，酚（而不是过氧自由基）的形成是甲苯氧化的主要途径，强调有必要重新评估其在大气中的臭氧和SOA形成的作用。
Photochemical oxidation of aromatic hydrocarbons leads to tropospheric ozone and secondary organic aerosol (SOA) formation, with profound implications for air quality, human health, and climate. Toluene is the most abundant aromatic compound under urban environments, but its detailed chemical oxidation mechanism remains uncertain. From combined laboratory experiments and quantum chemical calculations, we show a toluene oxidation mechanism that is different from the one adopted in current atmospheric models. Our experimental work indicates a largerthan-expected branching ratio for cresols, but a negligible formation of ring-opening products (e.g., methylglyoxal). Quantum chemical calculations also demonstrate that cresols are much more stable than their corresponding peroxy radicals, and, for the most favorable OH (ortho) addition, the pathway of H extraction by O-2 to form the cresol proceeds with a smaller barrier than O-2 addition to form the peroxy radical. Our results reveal that phenolic (rather than peroxy radical) formation represents the dominant pathway for toluene oxidation, highlighting the necessity to reassess its role in ozone and SOA formation in the atmosphere.