New particles in the atmosphere: two non-classical examples

大气中的新粒子：两个非经典例子

• 批准号: NE/E005659/1
• 负责人: John Plane
• 金额: $ 75.8万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FE005659%2F1
• 关键词: New; particles; atmosphere; two; non

Small particles play several very important roles in the atmosphere. They provide surfaces on which exotic chemical reactions can take place, and they act as the condensation nuclei ('seeds') on which water condenses to form ice particles and cloud droplets. Particles may also reflect visible and UV sunlight back to space (cooling the earth), and absorb outgoing infra-red radiation (contributing to the 'greenhouse' effect). For thermodynamic reasons (decreasing entropy), it is actually quite difficult to form new particles in the atmosphere from gaseous constituents. This process is known as homogeneous nucleation: a few molecules condense together to form a stable cluster (about 1 nm in size), which then becomes the building block for further growth. This proposal will examine two examples of homogeneous nucleation that occur in very different regions of the atmosphere: iodine oxide particles, which form in the marine boundary layer from iodine species that are produced biogenically in the ocean; and meteoric smoke particles, which form in the middle atmosphere from the metals and silicon oxides that ablate from meteoroids. For both these systems, we want to follow the evolution of the particles from single molecules to particles containing about 1 million molecules (diameter about 50 nm), in order to understand what controls the rate of growth and the shapes of the particles. Preliminary work shows that the particles are fractal-like ('fluffy'), with large surface areas which often facilitate chemical reactions. For example, meteoric smoke particles may influence some of the chemistry controlling ozone in the stratosphere. We will also examine the properties of these particles as ice condensation nuclei. Iodine oxides have recently been observed at high concentrations over coastal Antarctica, and could be a source of ice nuclei near the surface. Meteoric smoke particles are most likely the nuclei for noctilucent clouds. These ice clouds, which form around 83 km at high latitudes during mid-summer, were first observed at the end of the 19th Century. This has led to speculation that they are an early indicator of climate change in the middle atmosphere. Finally, we will address the question of how meteoric smoke particles descend from around 80 km to the earth's surface. The particles have been detected both by capturing them with a rocket-borne instrument flying above 70 km (in this project we propose to analyze some of these captured particles), and by detecting cosmic iridium and platinum in ice cores from Greenland and Antarctica. We will use the Met Office's general circulation model to study the transport pathways during present-day conditions and during a glacial maximum, in order to interpret the ice core record over several hundred thousand years.

小颗粒在大气中扮演多个非常重要的角色。它们提供了可以进行外来化学反应的表面，并充当凝结核（“种子”），水冷凝以形成冰颗粒和云滴。颗粒还可以反映可见的，紫外线阳光回到太空（冷却地球），并吸收外向红外辐射（有助于“温室”效应）。出于热力学原因（减少熵），从气体成分中形成大气中的新颗粒实际上很难。该过程称为均质成核：几个分子凝结在一起形成一个稳定的簇（大小约1 nm），然后成为进一步生长的基础。该提案将研究在大气中发生截然不同的区域中发生的两个均质成核的例子：碘氧化物颗粒，它们是在海洋边界层中由碘物种形成的，这些物种是在海洋中生物源产生的；和陨石颗粒，它们是在中间大气中由金属和硅氧化物中形成的。对于这两个系统，我们都希望遵循颗粒从单分子到包含约100万个分子（直径约50 nm）的颗粒的演变，以了解是什么控制了生长速率和颗粒形状。初步工作表明，颗粒是分形的（蓬松的），其表面积较大，通常会促进化学反应。例如，陨石颗粒可能会影响平流层中控制臭氧的某些化学。我们还将研究这些颗粒作为冰凝结核的特性。最近在沿海南极洲的高浓度下观察到碘氧化物，可能是表面附近的冰核的来源。气象烟颗粒很可能是夜光云的细胞核。这些冰云在仲夏时期最初在19世纪末观察到了大约83公里的高纬度。这导致人们猜测它们是中间气氛中气候变化的早期指标。最后，我们将解决一个问题，即流星烟颗粒如何从约80公里到地球表面下降。通过使用飞行在70 km以上的火箭式仪器捕获它们（在这个项目中，我们建议分析其中一些捕获的颗粒），以及通过检测来自格陵兰和南极洲的冰芯中的宇宙虹膜和铂，可以检测到这些颗粒。我们将使用MET办公室的一般循环模型在当今条件和冰川最大值期间研究运输途径，以便在数十万年内解释冰芯记录。