The reaction of oleic acid monolayers with gas-phase ozone at the air water interface: the effect of sub-phase viscosity, and inert secondary components.
The reaction of oleic acid monolayers with gas-phase ozone at the air water interface: the effect of sub-phase viscosity, and inert secondary components.
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DOI：
10.1039/d0cp03934a
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发表时间：
2020-12
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影响因子：
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通讯作者：
M. King;Stephanie H. Jones;C. O. Lucas;K. Thompson;A. Rennie;A. Ward;A. A. Marks-A.;F. N. Fisher;C. Pfrang;A. Hughes;R. Campbell
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文献类型：
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作者：
M. King;Stephanie H. Jones;C. O. Lucas;K. Thompson;A. Rennie;A. Ward;A. A. Marks-A.;F. N. Fisher;C. Pfrang;A. Hughes;R. Campbell
在大气颗粒物上形成的有机膜改变了颗粒物的光学和云凝结成核特性，因此对现代气候和气候模式具有影响。有机膜受到环境空气中存在的气相氧化剂的侵蚀。在这里，我们更详细地回顾了在空气-水界面的气相臭氧的油酸单层的氧化，因为这提供了一个模型系统的氧化反应发生在空气-水界面的含水大气气溶胶。在空气-液体界面处的油酸单层上在大气相关的臭氧浓度下进行实验，以研究子相的粘度是否影响反应速率，并确定单层内的第二组分硬脂酸的存在对反应动力学的影响，所述硬脂酸通常被认为对臭氧不反应，如通过中子反射计测量所确定的。大气中的气溶胶可能非常粘稠。反应的动力学被发现是独立的在一个范围内的中等粘度的单层以下的子相的粘度，证明没有参与的含水子相氧化剂的速率决定步骤。发现纯油酸单分子膜的氧化动力学取决于表面覆盖度，在油酸表面覆盖度为0.1 × 1018分子m-2的上下观察到不同的行为。大气气溶胶通常是复杂的混合物，并且在对直接臭氧氧化惰性的单层中存在另外的化合物硬脂酸，没有显著改变反应动力学。它表明，在空气-水界面的油酸单分子膜不留下任何可检测的材料在空气-水界面，矛盾的作者现在认为是错误的，在这个杂志上发表的以前的工作。这里提出的综合结果表明，动力学，从而大气化学寿命的不饱和表面活性物质在空气-水界面的损失与气相臭氧反应，可以被认为是独立的其他材料存在于空气-水界面或在水的子相。
Organic films that form on atmospheric particulate matter change the optical and cloud condensation nucleation properties of the particulate matter and consequently have implications for modern climate and climate models. The organic films are subject to attack from gas-phase oxidants present in ambient air. Here we revisit in greater detail the oxidation of a monolayer of oleic acid by gas-phase ozone at the air-water interface as this provides a model system for the oxidation reactions that occur at the air-water interface of aqueous atmospheric aerosol. Experiments were performed on monolayers of oleic acid at the air-liquid interface at atmospherically relevant ozone concentrations to investigate if the viscosity of the sub-phase influences the rate of the reaction and to determine the effect of the presence of a second component within the monolayer, stearic acid, which is generally considered to be non-reactive towards ozone, on the reaction kinetics as determined by neutron reflectometry measurements. Atmospheric aerosol can be extremely viscous. The kinetics of the reaction were found to be independent of the viscosity of the sub-phase below the monolayer over a range of moderate viscosities, , demonstrating no involvement of aqueous sub-phase oxidants in the rate determining step. The kinetics of oxidation of monolayers of pure oleic acid were found to depend on the surface coverage with different behaviour observed above and below a surface coverage of oleic acid of ∼1 × 1018 molecule m-2. Atmospheric aerosol are typically complex mixtures, and the presence of an additional compound in the monolayer that is inert to direct ozone oxidation, stearic acid, did not significantly change the reaction kinetics. It is demonstrated that oleic acid monolayers at the air-water interface do not leave any detectable material at the air-water interface, contradicting the previous work published in this journal which the authors now believe to be erroneous. The combined results presented here indicate that the kinetics, and thus the atmospheric chemical lifetime for unsaturated surface active materials at the air-water interface to loss by reaction with gas-phase ozone, can be considered to be independent of other materials present at either the air-water interface or in the aqueous sub-phase.