环烯烃臭氧化反应：二次臭氧化物的重要性和OH自由基生成机理

烯烃与臭氧的反应是大气中烯烃的重要清除途径，反应对颗粒物和大气OH自由基有很大的贡献，而环烯烃对颗粒物的贡献尤为显著。近几年中，在Criegee中间体(CIs)实验检测上取得的进展大大拓展了科学家对烯烃与臭氧反应研究，加深了对反应机理的理解。而本项目拟研究的是当前环烯烃和臭氧反应中被忽视了的另外两个重要问题：二次臭氧化物(SOZs)和OH自由基的生成机理。我们的初步理论计算表明，环烯烃中生成SOZs的可能性非常大，因为其CIs到SOZ的能垒远小于CI到OH自由基的能垒。本项目试图通过测量环烯烃与臭氧反应中SOZs和OH的产率来阐明环烯烃反应的特殊性。除了在大气化学中的意义之外，本研究也有助于我们评估萜烯对室内空气质量和人体健康。室内环境中通常存在较高浓度的环状萜烯，它们与臭氧反应可能生成较大量的SOZs，而SOZs通常又具有高氧化性而可能危害人体健康。

The reaction of alkenes and ozone is the key removal of alkenes in the atmosphere. The oxidation contributes significantly to the formation of particulate matter and OH radical in the atmosphere, especially the oxidation of cycloalkenes. In recent years, the advances in detection of Criegee intermediates (CIs) have greatly widened the studies on the reactions of alkenes and ozone, and also advanced our understanding on the reaction mechanism. However, we propose in this project to attack two other important problems in ozonolysis reaction of cycloalkenes, e.g., the formation of secondary ozonides (SOZs) and the formation mechanism of OH radical, which have been largely ignored and overlooked. Our preliminary calculations show that the CIs from ozonolysis of cycloalkenes might have great tendency in forming SOZs because the barriers heights for SOZ formation are usually far lower than those for OH formation. We propose to measure the formation yields for both SOZs and OH radicals, attempting to reveal the characteristics in ozonolysis of cycloalkenes. Besides the significances in the atmospheric chemistry of cycloalkenes, our proposed studies would also help us to evaluate the impact on indoor air quality and possible hazards on human health from terpenes. Indoor air usually contains high concentration of cyclic terpenes, which can possibly form a large amount of SOZs when reacting with ozone; while the high oxidizing power of SOZs suggests their potential harm to human health.