氮氧化物作用下α-蒎烯臭氧化反应生成二次有机气溶胶的机制研究

α-Pinene is one of key atmospheric biogenic volatile organic compounds（VOCs）emitted by vegetation, and its reaction with ozone contributes significantly to the formation of secondary organic aerosols (SOA). Nitrogen oxides (NOx), which is ubiquitous in the atmosphere, can impact SOA formation from α-pinene ozonolysis by disturbing the reactions of key intermediates such as organic peroxy (RO2) radicals and stabilized Criegee intermediates (sCI). However, currently the molecular composition and formation and growth mechanisms of SOA from α-pinene ozonolysis in the presence of NOx is poorly constrained. This project will address the processes that lead to the formation and growth of SOA from α-pinene ozonolysis in the presence of NOx, with an integration of laboratory experiments and kinetic model simulations. The formation and distribution of major SOA compositions and their relation to NOx concentrations will be quantitatively probed, as well as kinetic parameters of critical chemical processes. The key mechanisms of SOA formation and growth will be developed. The results of this project will advance our knowledge of atmospheric oxidation of α-pinene and its contribution to SOA formation. In addition, the results will benefit the development of relevant atmospheric chemistry models and the assessment of the role of biogenic emissions in air pollution and climate change.

α-蒎烯是大气中一种重要的天然源挥发性有机物（VOCs），其与臭氧反应对大气二次有机气溶胶（SOA）具有重要贡献。氮氧化物（NOx）与α-蒎烯在大气中普遍共存。NOx可以改变α-蒎烯臭氧化反应中有机过氧自由基（RO2）和稳定化的Criegee中间体（sCI）的反应途径，进而影响SOA的形成，但是目前NOx作用下α-蒎烯臭氧化反应SOA组分分布与生成机制尚不十分清楚。本项目将以实验室模拟为主，结合动力学模型模拟，研究NOx存在条件下α-蒎烯臭氧化反应，探究SOA的生成及重要组分分布与NOx浓度水平的定量关系，探究臭氧化反应中关键化学过程的反应动力学参数，揭示SOA生成和增长的关键机制。研究结果有助于认识α-蒎烯大气氧化反应对SOA的贡献，对于建立和完善相关大气化学模型、准确评估天然源VOCs对大气环境和气候变化的影响具有重要意义。

天然源挥发性有机物―α-蒎烯与臭氧反应是大气二次有机气溶胶（SOA）的重要来源。在实际大气中，α-蒎烯的氧化普遍受到氮氧化物（NOx）的显著影响。因此，准确评估α-蒎烯对大气SOA的贡献需要弄清NOx影响下其氧化生成SOA的机制。本项目采用实验室模拟和动力学模式模拟相结合的手段，开展了NOx影响下α-蒎烯臭氧化反应生成SOA的机理研究。揭示了过氧自由基（RO2）碰并反应生成ROOR二聚体和酰基RO2自由基反应生成酯类二聚体是低挥发性有机物生成的关键路径。明晰了NO和NO2通过清除RO2或酰基RO2自由基（而非Criegee自由基）而抑制低挥发性二聚体的生成是其影响SOA形成的关键机制。阐明了NOx对α-蒎烯SOA中二聚体、有机过氧化物和有机硝酸酯等组分分布和多相反应活性的影响。同时确定了α-蒎烯酰基RO2自由基与NO2反应的平均速率常数范围（1.2×10^-12~3×10^-11cm3 molecule-1 s-1）。该项目的成果增进了对α-蒎烯大气氧化生成SOA机制的认识，也可为探索和评估天然源排放与人为源污染物之间的交互作用及其环境和气候影响提供基础数据。