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。

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.