Phase state and diffusion within atmospheric particles

生物来源（如植被）和人为来源（如交通）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，形成半挥发性有机化合物，然后低挥发性产物冷凝并形成微观颗粒。我们将这些微观颗粒称为次生有机物质（SOM）颗粒。“次级”一词是指该物质是在大气中形成的，而不是直接排放到大气中。SOM颗粒可以通过散射和吸收太阳辐射以及作为云的种子（即核）来影响地球的气候。SOM颗粒也会对空气质量和人类健康产生负面影响。目前，对SOM颗粒的科学认识还很低，这限制了我们预测其对气候，空气质量和健康影响的能力。最近的研究表明，SOM颗粒的质量，尺寸，反应性，光学性质和云成核性质的预测是敏感的以下属性：1）有机物在SOM颗粒内的分子扩散，2）玻璃形成的SOM颗粒和3）液-液相分离的SOM颗粒。 本提案侧重于这三个关键属性。我们将直接测量SOM颗粒内有机物的分子扩散速率。结果将被用来量化的斯托克斯-爱因斯坦方程，这是经常被用来估计有机物在SOM颗粒的扩散速率的准确性。此外，我们将进行第一次直接测量的有机物内SOM的扩散速率在温度低于293 K，相关的大部分大气的温度范围。我们还将确定大气中单个SOM颗粒变成玻璃（与玻璃窗格相同的物理状态）的条件。 最后，我们将确定SOM颗粒进行液-液相分离以在单个颗粒内形成两种液体（富水液体和富有机物液体）的条件。我们希望这些结果将被用于其他人时，预测的质量，尺寸，反应性，光学特性和云成核特性的SOM颗粒在大气中。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.