Phase state and diffusion within atmospheric particles

生物来源(例如植被)和人为来源(例如运输)排放大量挥发性有机化合物。在大气中，这些挥发性有机化合物通过一系列复杂的反应被氧化成半挥发性有机化合物，然后低挥发性产物缩合并形成微观颗粒。我们将这些微观颗粒称为次生有机物质(SOM)颗粒。术语“二次”表示物质是在大气中形成的，而不是直接排放到大气中。SOM粒子可以通过散射和吸收太阳辐射以及作为云的种子(即核)来影响地球气候。SOM颗粒还会对空气质量和人体健康产生负面影响。目前对SOM颗粒的科学认识很低，这限制了我们预测它们对气候、空气质量和健康的影响的能力。 最近的研究表明，对SOM颗粒的质量、大小、反应性、光学性质和云成核性质的预测对以下性质很敏感：1)有机物在SOM颗粒内的分子扩散，2)SOM颗粒内玻璃的形成，3)SOM颗粒内的液-液分离。这项建议侧重于这三个关键属性。我们将直接测量有机物在SOM颗粒中的分子扩散速率。结果将被用来量化斯托克斯-爱因斯坦方程的准确性，该方程经常被用来估计有机物在SOM颗粒中的扩散速度。此外，我们将首次在低于293K的温度范围内直接测量有机物在SOM内的扩散速度，这一温度范围与大部分大气有关。我们还将确定大气中单个SOM颗粒成为玻璃的条件(与玻璃窗玻璃的物理状态相同)。最后，我们将确定SOM颗粒通过液-液相分离在单个颗粒中形成两种液体(富水液体和富有机液体)的条件。我们预计这些结果将被其他人用来预测大气中SOM粒子的质量、大小、反应性、光学性质和云核性质。简而言之，这些结果将对未来许多大气化学和气候的模拟研究具有重要意义。

Biological sources (for example vegetation) and anthropogenic sources (for example transportation) emit copious quantities of volatile organic compounds. In the atmosphere, these volatile organic compounds are oxidized by a complex series of reactions to form semivolatile organic compounds, followed by condensation of the low volatility products and formation of microscopic particles. We refer to these microscopic particles as secondary organic material (SOM) particles. The term “secondary” indicates the material is formed in the atmosphere rather than emitted directly into the atmosphere. SOM particles can affect Earth's climate by scattering and absorbing solar radiation and by acting as seeds (i.e. nuclei) for clouds. SOM particles can also negatively affect air quality and human health. Currently the scientific understanding of SOM particles is low, which limits our ability to predict their impact on climate, air quality and health. Recent studies have shown that predictions of the mass, size, reactivity, optical properties and cloud nucleating properties of SOM particles are sensitive to the following properties: 1) molecular diffusion of organics within SOM particles, 2) glass formation within SOM particles and 3) liquid-liquid phase separation within SOM particles. This proposal focuses on these three key properties. We will directly measure molecular diffusion rates of organics within SOM particles. The results will be used to quantify the accuracy of the Stokes-Einstein equation, which is often used to estimate diffusion rates of organics in SOM particles. In addition, we will carry out the first direct measurements of diffusion rates of organics within SOM at temperatures less than 293 K, a temperature range relevant to a large part of the atmosphere. We will also determine conditions at which individual SOM particles in the atmosphere become a glass (the same physical state as a glass window pane). Finally, we will determine conditions at which SOM particles undergo liquid-liquid phase separation to form two liquids (a water-rich liquid and an organic-rich liquid) within individual particles. We expect these results will be used by others when predicting the mass, size, reactivity, optical properties and cloud nucleating properties of SOM particles in the atmosphere. In short, these results will be important to many future modelling studies of atmospheric chemistry and climate.