Formation of Highly Oxygenated Organic Molecules from α-Pinene Ozonolysis: Chemical Characteristics, Mechanism, and Kinetic Model Development
Formation of Highly Oxygenated Organic Molecules from α-Pinene Ozonolysis: Chemical Characteristics, Mechanism, and Kinetic Model Development
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DOI：
10.1021/acsearthspacechem.9b00035
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发表时间：
2019-05-01
影响因子：
3.4
通讯作者：
Dommen, Josef
中科院分区：
文献类型：
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作者：
Molteni, Ugo;Simon, Mario;Dommen, Josef
萜类化合物是由植物排放的，其在大气中的氧化是二次有机气溶胶(SOA)的重要来源。这种氧化的一部分可以通过自氧化过程进行，产生低饱和蒸气压的高含氧有机分子(HOMS)。因此，即使在没有硫酸的情况下，它们也可以促进新粒子的形成(NPF)。对自氧化反应的机理和动力学的了解还远远不够。在这里，我们提出了对欧洲核子研究中心云8活动期间进行的α-蒎烯(AP)臭氧分解实验的质谱学数据进行的机理和动力学分析。我们根据确定的化学成分将HOM分组，并研究了这些基团及其组分随试剂浓度的相对变化。我们测定了不同HOM过氧基反应途径的反应速率常数。Hom-peroxy自由基之间的吸附反应速度极快。我们开发了一个生成HOM的伪机理，并将其添加到主化学机理(MCM)的AP氧化方案中。利用该扩展模型，成功地模拟了HOM形成过程中的观测浓度和变化趋势。
Terpenes are emitted by vegetation, and their oxidation in the atmosphere is an important source of secondary organic aerosol (SOA). A part of this oxidation can proceed through an autoxidation process, yielding highly oxygenated organic molecules (HOMs) with low saturation vapor pressure. They can therefore contribute, even in the absence of sulfuric acid, to new particle formation (NPF). The understanding of the autoxidation mechanism and its kinetics is still far from complete. Here, we present a mechanistic and kinetic analysis of mass spectrometry data from alpha-pinene (AP) ozonolysis experiments performed during the CLOUD 8 campaign at CERN. We grouped HOMs in classes according to their identified chemical composition and investigated the relative changes of these groups and their components as a function of the reagent concentration. We determined reaction rate constants for the different HOM peroxy radical reaction pathways. The accretion reaction between HOM peroxy radicals was found to be extremely fast. We developed a pseudo-mechanism for HOM formation and added it to the AP oxidation scheme of the Master Chemical Mechanism (MCM). With this extended model, the observed concentrations and trends in HOM formation were successfully simulated.