研究报告
薛婧雯,马芳芳,谢宏彬.·Cl引发α-蒎烯的大气氧化机制及动力学[J].环境科学学报,2022,42(12):262-272
·Cl引发α-蒎烯的大气氧化机制及动力学
- Atmospheric oxidation mechanism and kinetics of α-pinene initiated by ·Cl
- 基金项目：国家自然科学基金面上项目（21876024）
- 作者
- 单位
- 薛婧雯
- 大连理工大学环境学院，工业生态与环境工程教育部重点实验室，大连 116024
- 马芳芳
- 大连理工大学环境学院，工业生态与环境工程教育部重点实验室，大连 116024
- 谢宏彬
- 大连理工大学环境学院，工业生态与环境工程教育部重点实验室，大连 116024
- 摘要：α-蒎烯是大气中含量最丰富的单萜烯类挥发性有机化合物，与氯自由基（·Cl）反应是其重要的转化途径.然而，·Cl引发α-蒎烯大气氧化的分子机制尚不清楚.本研究采用量子化学计算与微观动力学模拟相结合的方法，研究了·Cl与α-蒎烯的引发反应以及引发反应生成的主要α-蒎烯自由基的后续转化机制与动力学.结果发现，·Cl反式加成到α-蒎烯的C2位置生成加成中间体IM1-9-a是最可行的反应途径.在298 K和1.013×105 Pa条件下，计算得到·Cl与α-蒎烯的反应速率常数（kCl）为3.1×10-10 cm3·molecule-1·s-1，与kCl的实验值（4.6±1.3）×10-10 cm3·molecule-1·s-1一致.生成的IM1-9-a进一步与O2反应生成过氧自由基IM3-1-a，在2.5×109 cm-3（100 ppt） NO和1.25×109 cm-3（50 ppt） HO2·条件下，IM3-1-a后续主要与NO和HO2·反应生成有机硝酸酯（C10H16ClNO3和C10H16ClNO4）、氢过氧化物（C10H17ClO2和C10H17ClO3）和烷氧自由基（C10H16ClO2·）.生成的 闭壳层产物与母体α-蒎烯相比具有较高的O∶C比，可能具有较低的蒸气压，进而贡献二次有机气溶胶.本研究结果可为全面评价α-蒎烯的 大气化学反应对大气质量的影响提供理论支撑.
- Abstract：α-pinene is the most abundant monoterpene volatile organic compounds in the atmosphere， and reaction with chlorine radicals （·Cl） has been considered an important sink for it. However， the atmospheric oxidation mechanism of ·Cl initiated reactions of α-pinene remains unknown. Herein， the initial reaction of α-pinene with ·Cl， and subsequent reactions of resulting α-pinene-radicals， were investigated by a combination of quantum chemical calculations and kinetics modeling. The results indicate that ·Cl anti-addition to the C2 position of α-pinene forming intermediate IM1-9-a is the dominant pathway for the initial ·Cl + α-pinene reaction. At 298 K and 1.013×105 Pa， the calculated overall reaction rate constant （kCl） for the ·Cl + α-pinene reaction is 3.1×10-10 cm3·molecule-1·s-1， which is close to the available experimental value （4.6±1.3）×10-10 cm3·molecule-1·s-1. The favorably formed IM1-9-a further react with O2 to produce peroxy radicals IM3-1-a， which mainly react with NO and HO2? under 2.5×109 cm-3（100 ppt） NO and 1.25×109 cm-3（50 ppt） HO2? conditions， to form organonitrates（C10H16ClNO3/C10H16ClNO4）， hydroperoxide products（C10H17ClO2/C10H17ClO3） and alkoxy radicals（C10H16ClO2·）. The formed closed-shell products have high oxygen-to-carbon ratios compared to the parent α-pinene and therefore are expected to have lower vapor pressures， which can contribute to the formation of secondary organic aerosol. Overall， our work provides theoretical support for a comprehensive evaluation of the impacts of atmospheric chemical reactions of α-pinene on air quality.
- Key words：α-pinene chlorine radicals quantum chemical calculation atmospheric oxidation mechanism kinetics
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