Characteristics of Organic Microlayer Produced AerosolS

海洋表面通过产生直径从100纳米到几微米的海洋喷雾气溶胶颗粒，与云的辐射特性密切相关，这些颗粒随后成为云滴形成的场所。云滴的数量高度依赖于进入云的粒子的数量、大小和组成。大小和组成决定了液滴的表面张力和化学活性，这是决定气溶胶颗粒是否会形成云滴的关键参数。云滴数浓度反过来又控制着云的辐射特性，云滴数越大，云的反射性越强。这会改变到达地表的辐射量，并对区域和全球地表温度产生影响。所描述的联系很少被量化，而且提供了政府间气候变化专门委员会（IPCC）目前评估的最不确定的气候强迫。海洋表面富含有机物，这些有机物是由存在于表层水中的微生物产生的。生物碎屑具有明显的疏水性，像油一样，在表面形成一层膜。这种有机表面薄膜已经被发现有一段时间了，它可能改变了气体物质的海气交换率，也改变了海洋的表面张力。与这一建议最相关的是，含有有机物质的颗粒可能是由风驱动的海洋表面上的白帽破裂产生的。以前，云建模者认为，海洋喷雾产生的颗粒由无机盐组成，类似于散装海水，主要是氯化钠。然而，最近发表在《自然》杂志上的研究表明，在海洋大气中占主导地位的积聚模式（大小在100 nm至1 um之间）颗粒中含有非常丰富的来自SSML的有机物质。有机物种具有非常不同的表面张力和化学活动，这就是为什么它们首先被分割到海洋表面的原因，因此可以预期形成的颗粒将与氯化钠具有非常不同的性质。该提案旨在收集SSML中的有机物质，确定主要的生物物种，培养它并生物合成大量的物质。这种合成产品在化学上与SSML中的有机物相似，将作为气溶胶喷射到一个大的腔室中，可以单独使用，也可以与硫酸盐和/或氯化钠混合使用，并使用各种最先进的仪器来研究其物理和化学特性，包括其形成云滴的能力，从而研究其对颗粒特性的影响。这些数据将用于测试我们在曼彻斯特开发的气溶胶颗粒特性的详细模型。一旦我们使用实验室生成的数据约束了模型，就会进行一系列模拟，以测试实验室的发现对海洋边界层云的可能影响。显然有必要进行这项工作，以减少我们对浅海云中云滴数估计的不确定性，浅海云中云滴是一种辐射上特别重要的云类型。此外，表层海洋、云和气候之间有直接的联系。据推测，海洋生物群可能对气候变化很敏感，而生物的变化可能以一种高度不确定的方式对气溶胶和云的特性产生重大影响。这种变化的迹象仍然未知，如果我们要预测未来对气候的影响以及未来海洋与气候变化之间的联系，我们需要量化这种可变性。

The surface of the ocean is closely coupled to the radiative properties of clouds through the generation of sea spray aerosol particles that range from 100 nm to several um in diameter and which subsequently act as sites for cloud droplet formation. The number of cloud droplets is highly dependent on the number, size and composition of particles entering the cloud. The size and composition determine the surface tension and chemical activity of the drops, key parameters in determining whether an aerosol particle will form a cloud droplet or not. The cloud droplet number concentration in turn controls the radiative properties of the cloud, the greater the droplet number, the more reflective the cloud. This can change the amount of radiation reaching the surface and impact on regional and global surface temperatures. The links described are very poorly quantified and provide the most uncertain forcings of climate that are currently assessed by the Intergovernmental Panel on Climate Change (IPCC). The ocean surface is rich in organic material resulting from micro-organisms that are present in the surface waters. Biological detritus is significantly hydrophobic and, like oil, partitions to the surface forming a film. Such organic surface films have been known about for some time and may be responsible for changing air-sea exchange rates of gaseous material and also altering the surface tension of the sea. Most relevant to this proposal is that particles containing organic material may be produced by the action of wind driven white caps breaking on the ocean surface. Previously, cloud modellers have considered sea spray derived particles to be composed of inorganic salts similar to bulk seawater, predominately sodium chloride. However, recent work published in Nature has shown that the particles in the accumulation mode (between 100 nm and 1 um in size) which dominate the particle number in the marine atmosphere are very rich in organic material from the SSML. Organic species have very different surface tensions and chemical activities which is why they partition to the surface of the ocean in the first place, hence it is to be expected that the formed particles will have very different properties from sodium chloride. This proposal seeks to harvest the organic material in the SSML, determine the major biological speciation, culture it and biologically synthesise significant quantities of the material. This synthesised product, which will be chemically similar to the organic in the SSML, will be sprayed into a large chamber as an aerosol, either on its own or mixed with sulphate and/or sodium chloride and its impact on particle properties studied using a wide range of state of the art instrumentation to probe its physical and chemical properties, including its ability to form cloud droplets. These data will be used to test a detailed model of the properties of the aerosol particles we have developed at Manchester. Once we have constrained the model using the laboratory generated data, a series of simulations will be conducted to test the likely impact the findings from the laboratory will have on clouds in the marine boundary layer. There is a clear need to perform this work to reduce the uncertainty in our estimates of cloud droplet number in shallow marine clouds, a particularly radiatively important cloud type. Furthermore, there is a direct link between the surface ocean, clouds and climate. It has been postulated that marine biota are likely to be sensitive to climate change and a change to the biology may significantly impact on the aerosol and hence cloud properties in a highly uncertain way. The sign of such a change remains unknown, and we need to quantify such variability if we are to predict future impacts on climate and linkages between the ocean and climate changes in the future.