Aerosol Characterisation and Modelling in the Marine Environment (ACMME)

气溶胶粒子在气候强迫中起着重要作用，但控制其行为的过程仍然不确定。海洋覆盖地球表面的大部分，已知会产生不同化学性质的颗粒物质（海盐、有机物质和硫酸盐），但对不同气溶胶类型的范围和气候影响知之甚少。最近，人们对海洋颗粒的有机成分产生了相当大的兴趣。有人认为，海雾衍生粒子含有大量的有机物产生的机械从海面微层，可以显着影响云的形成潜力。气溶胶颗粒吸收水的能力，即其吸湿性，是一个非常重要的性质，因为这将增加亚饱和环境中的颗粒尺寸（从而增加散射潜力），并且还决定了它们是否会充当有效的云凝结核（CCN）。这种性质由颗粒尺寸和组成决定。虽然无机部分的吸湿行为相对较好地理解，但我们对有机部分的行为的了解远未得到很好的发展。一般来说，有机物不是特别吸湿的。然而，已知许多种类的有机化合物抑制表面张力。在多组分气溶胶中，这种性质导致在云中激活所需的过饱和度降低，从而改变形成的液滴数量。由于海洋有机部分的这种潜在意义，这是至关重要的，这一组成部分是更好地表征和其空间分布评估，使其在气候过程中的作用量化。此外，已知海洋环境中的颗粒物会对大气的化学性质产生重大影响。目前，人们对气溶胶在卤素通过多相过程循环中的作用有很大的研究兴趣，这可以显著改变地球大气中臭氧和其他氧化剂的浓度。这些过程的速率取决于可用的颗粒表面积和颗粒的酸度，两者都很难表征。为了解决海洋气溶胶作用的不确定性，ACMME将准确地量化地球仪中特征不明确的区域中颗粒物的化学和物理特性，使用最先进的模型中的这些结果来预测这些气溶胶的特性及其对云滴形成的影响。这些测量将在2007年里斯本和佛得角群岛之间由英国SOLAS资助的海上边界层反应性卤素（RHaMBLe）内的NERC研究船Discovery上进行。ACMME将对气溶胶形成云凝结核的能力、云激活潜力和取样气溶胶的吸湿增长进行直接测量和模型预测。前者在确定间接辐射效应方面起主要作用，后者在确定直接效应方面起主要作用。将利用在联合王国《海上人命安全公约》资助的项目《评估》下开发的一个新模式，预测多组分海洋气溶胶对云滴数的影响。类似地，额外的成分数据将用于提供对对流层氧化剂收支具有重要意义的非均相反应速率的约束。对成分、混合状态和环境水含量的测量将与相关提案中的化学模拟活动结合使用，以评估它们在控制海洋大气中卤素循环的多相化学过程中的重要性。最后，还将把这些数据与调查人员和其他人在海上进行的类似大气研究的数据进行比较，以评估海洋气溶胶特性的空间变异性及其影响。

Aerosol particles play an important role in climate forcing but the processes governing their behaviour still remain uncertain. Oceans, which cover the majority of the earth's surface, are known to generate particulate matter of different chemical natures (sea salt, organic material and sulphate) but the extents and climactic implications of the different aerosol types are very poorly understood. More recently there has been considerable interest in the organic component of marine particles. It has been suggested that that seaspray derived particles contain large quantities of organic matter generated mechanically from the sea surface microlayer which can influence cloud forming potential significantly. The ability of an aerosol particle to take up water, its hygroscopicity, is a highly important property, as this will increase particle size (and therefore scattering potential) in sub-saturated environments and also dictates whether they will act as an effective Cloud Condensation Nucleus (CCN). This property is determined by particle size and composition. Whilst the hygroscopic behaviour of the inorganic fraction is relatively well understood, our knowledge of the behaviour of the organic fraction is far less well developed. Organic matter in general is not particularly hygroscopic. However many classes of organic compounds are known to suppress surface tension. In multicomponent aerosol, this property leads to a reduction in the supersaturation required to activate in a cloud, modifying the number of droplets formed. Because of this potential significance of the marine organic fraction, it is vital that this component is better characterised and its spatial distribution evaluated so allowing quantification of its role in climatic processes. In addition, particulate matter from marine environments is known to significantly affect the chemistry of the atmosphere. There is significant current research interest in the roles of aerosols in halogen cycling through heterogeneous processes, which can significantly alter the concentrations of ozone and other oxidants in the Earth's atmosphere. The rates of these processes depend on the available particulate surface area and the acidity of the particles, both poorly characterised. To address the uncertainty in the roles of marine aerosol, ACMME will accurately quantify the chemical and the physical properties of particulate matter in a poorly characterised region of the globe, using these results in state of the art models to predict properties of these aerosol and their impacts on cloud droplet formation. These measurements will be made onboard the NERC research vessel Discovery, on the 2007 cruise between Lisbon and the Cape Verde Islands funded by UK SOLAS within the Reactive Halogens in the Marine Boundary Layer (RHaMBLe). ACMME will make direct measurements and model predictions of the ability of an aerosol to form a CCN, the cloud-activation potential, and hygroscopic growth of the sampled aerosol. The former plays a major role in determining the indirect radiative effect and the latter, the direct effect. Predictions of the effect of multicomponent marine aerosol on cloud droplet number will be made using a new model developed under the UK-SOLAS funded project APPRAISE. Similarly, additional compositional data will be used to provide constraint on the heterogeneous reaction rates which have significance in the tropospheric oxidant budget. The measurements of compositions, mixing states and ambient water contents will be used in conjunction with chemical modelling activities in associated proposals to assess their importance in the heterogeneous chemical processes that control halogen cycling in the marine atmosphere. Finally, the data will also be compared with those from similar atmospheric studies at sea, both by the investigators and others, in order to assess the spatial variability of marine aerosol properties and their effects.