Department of Physics, Tampere University of Technology, P O Box 692, 33101 Tampere, Finland.
Nature. 2010 Oct 14;467(7317):824-7. doi: 10.1038/nature09455.
Secondary organic aerosol (SOA) particles are formed in the atmosphere from condensable oxidation products of anthropogenic and biogenic volatile organic compounds (VOCs). On a global scale, biogenic VOCs account for about 90% of VOC emissions and of SOA formation (90 billion kilograms of carbon per year). SOA particles can scatter radiation and act as cloud condensation or ice nuclei, and thereby influence the Earth's radiation balance and climate. They consist of a myriad of different compounds with varying physicochemical properties, and little information is available on the phase state of SOA particles. Gas-particle partitioning models usually assume that SOA particles are liquid, but here we present experimental evidence that they can be solid under ambient conditions. We investigated biogenic SOA particles formed from oxidation products of VOCs in plant chamber experiments and in boreal forests within a few hours after atmospheric nucleation events. On the basis of observed particle bouncing in an aerosol impactor and of electron microscopy we conclude that biogenic SOA particles can adopt an amorphous solid-most probably glassy-state. This amorphous solid state should provoke a rethinking of SOA processes because it may influence the partitioning of semi-volatile compounds, reduce the rate of heterogeneous chemical reactions, affect the particles' ability to accommodate water and act as cloud condensation or ice nuclei, and change the atmospheric lifetime of the particles. Thus, the results of this study challenge traditional views of the kinetics and thermodynamics of SOA formation and transformation in the atmosphere and their implications for air quality and climate.
次生有机气溶胶（SOA）颗粒是在大气中由人为和生物挥发性有机化合物（VOC）的可凝结氧化产物形成的。在全球范围内，生物源 VOC 占 VOC 排放和 SOA 形成的 90%（每年 900 亿公斤碳）。SOA 颗粒可以散射辐射，并作为云凝结核或冰核，从而影响地球的辐射平衡和气候。它们由具有不同物理化学性质的无数不同化合物组成，关于 SOA 颗粒的相态状态的信息很少。气粒分配模型通常假设 SOA 颗粒为液态，但这里我们提供的实验证据表明，它们在环境条件下可以为固态。我们通过在植物腔室实验和在大气成核事件发生后的几个小时内在北方森林中研究了由 VOC 氧化产物形成的生物源 SOA 颗粒。基于在气溶胶撞击器中观察到的颗粒反弹和电子显微镜，我们得出结论，生物源 SOA 颗粒可以采用无定形固体-很可能是玻璃态。这种无定形固体状态应该会促使重新思考 SOA 过程，因为它可能会影响半挥发性化合物的分配，降低异相化学反应的速率，影响颗粒容纳水的能力并充当云凝结核或冰核，并改变颗粒在大气中的寿命。因此，这项研究的结果挑战了传统的 SOA 形成和转化的动力学和热力学观点，以及它们对空气质量和气候的影响。
