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着几个非常重要的角色。它们提供了可以发生奇异化学反应的表面，它们充当凝结核（“种子”），水在上面凝结形成冰粒和云滴。粒子还可能将可见光和紫外线反射回太空（使地球降温），并吸收向外的红外辐射（造成“温室”效应）。由于热力学的原因（熵的减少），在大气中由气体成分形成新粒子实际上是相当困难的。这个过程被称为均匀成核：一些分子凝聚在一起形成一个稳定的簇（大约1纳米大小），然后成为进一步生长的基石。本建议将研究发生在大气非常不同区域的两个均匀成核的例子：氧化碘粒子，它是由海洋生物产生的碘种在海洋边界层中形成的；还有流星烟雾颗粒，它是由流星中烧蚀的金属和硅氧化物在大气中形成的。对于这两个系统，我们想要跟踪粒子从单个分子到包含大约100万个分子（直径约50纳米）的粒子的演变，以便了解是什么控制了生长速度和粒子的形状。初步研究表明，这些颗粒呈分形状（“蓬松”），具有较大的表面积，通常有助于化学反应。例如，大气烟雾颗粒可能会影响平流层中控制臭氧的一些化学物质。我们还将研究这些粒子作为冰凝结核的性质。最近在南极洲沿海观测到高浓度的碘氧化物，它可能是地表附近冰核的一个来源。流星烟雾粒子最有可能是夜光云的核。这些冰云是在19世纪末首次被观测到的，它们在盛夏的高纬度地区形成约83公里。这导致人们猜测，它们是中层大气气候变化的早期指标。最后，我们将讨论大气烟雾粒子是如何从大约80千米的高空降至地球表面的。这些粒子是通过在70公里高空飞行的火箭载仪器捕获的（在这个项目中，我们打算分析其中一些捕获的粒子），以及通过在格陵兰岛和南极洲的冰芯中探测宇宙铱和铂来探测的。我们将使用英国气象局的环流模型来研究在当前条件下和在冰期极大期的运输路径，以便解释几十万年来的冰芯记录。