Reducing the Uncertainties in Aerosol Hygroscopic Growth

气溶胶和云是地球大气层的重要组成部分，影响辐射收支和化学成分，并影响人类健康。事实上，气溶胶和云对全球气候的影响仍然是理解以前的气候观测和预测未来气候变化的最大单一不确定性之一。气溶胶和云可以散射和吸收太阳光和地面辐射，通过改变入射太阳辐射和出射红外光的平衡对气候产生直接影响。气溶胶对气候有间接影响，影响云的寿命和寿命。所有的云滴都是由小得多的气溶胶粒子种子形成的，水可以在这些粒子上凝结。地球大气中气溶胶粒子数量及其大小分布的变化会导致云滴数量的变化。此外，一些气溶胶（如无机盐）比其他气溶胶（如不溶于水的有机化合物）更具吸湿性，因此对水的亲和力不同，改变了云滴形成的条件。气溶胶对气候的这种间接影响没有受到很好的限制，通常会抵消大气中温室气体水平增加引起的变暖，对地球气候产生冷却作用。在这个项目中，我们将研究一些控制气溶胶对水的亲和力的因素，以及它们作为云凝结核的能力。我们将模拟由光或电场捕获的单个粒子的气溶胶过程，以高时间分辨率（优于10 ms）和高精度（优于+/-0.5%）测量它们的演变尺寸。更具体地说，这项研究将分为三个较小的工作包。在第一个工作包中，我们将评估和完善目前用于量化气溶胶颗粒对水的亲和力的热力学模型。测量将使我们能够确定粒子大小随相对湿度的变化，其准确度比以前更高，甚至可以达到云滴形成的条件。这些新的数据记录从气溶胶粒子含有广泛的有机和无机溶质的典型成分在大气中发现，将提供更大的约束模型气溶胶粒子的增长到云滴。在第二个工作包，我们将调查的因素，控制的平衡和随时间变化的组成的表面的一个不断增长的云滴。表面成分不同于整体成分，它在决定气溶胶粒子成为云滴的容易程度方面至关重要。目前的表面成分（张力）模型基于非常少的数据，并将作为本项目测量的结果进行改进。在最终的工作包中，我们将模拟和测量云滴增长的动力学，特别是检查有机化合物在增长的水滴上的凝结，可以伴随着水的凝结。这一点最近被强调为一个在很大程度上被忽视的重要影响。改进对有机化合物凝结动力学的量化，将能更好地预测云滴数量，其敏感性将通过云块模型进行测试，总之，该项目将设法减少在量化大气气溶胶粒子上发生的微物理过程及其对云的影响方面的一些不确定性。

Aerosols and clouds are important components of the Earth's atmosphere, influencing the radiation budget and chemical composition, and impacting on human health. Indeed, the impact of aerosols and clouds on global climate remains one of the largest single uncertainties in understanding previous climate observations and in predicting future climate change. Aerosols and clouds can scatter and absorb sunlight and terrestrial radiation, having a direct effect on climate by altering the balance of incoming solar radiation and outgoing infrared light. Aerosols have an indirect effect on climate, influencing the albedo and lifetime of clouds. All cloud droplets form from the much smaller aerosol particle seeds on which water can condense. Changes in the number of aerosol particles in the Earth's atmosphere and their size distribution can lead to changes in the number of cloud droplets that form. In addition, some aerosols (such as inorganic salts) are considerably more hygroscopic than others (such as water insoluble organic compounds) and therefore have different affinities for water, changing the conditions under which cloud droplet formation can occur. This indirect effect of aerosols on climate is poorly constrained and generally counteracts the warming induced by increased levels of greenhouse gases in the atmosphere, exerting a cooling effect on the Earth's climate.In this project we will examine some of the factors that control the affinity of aerosol for water and their ability to act as cloud condensation nuclei. We will simulate aerosol processes on single particles trapped by either light or electrical fields, measuring their evolving size with high time-resolution (better than 10 ms) and high accuracy (better than +/- 0.5 %). More specifically, the research will be divided into three smaller work packages.In the first work package, we will assess and refine the current thermodynamic models for quantifying the affinity of aerosol particles for water. Measurements will allow us to determine the change in particle size with relative humidity with considerably better accuracy than has previously been possible even up to the conditions under which cloud droplets form. Recorded from aerosol particles containing a wide range of organic and inorganic solutes typical of components found in the atmosphere, these new data will provide greater constraints for modelling the growth of aerosol particles into cloud droplets.In a second work package, we will investigate the factors that control the equilibrium and time-dependent composition of the surface of a growing cloud droplet. The surface composition, which differs from the bulk, is crucial in determining how facile it is for aerosol particles to become cloud droplets. Current models of surface composition (tension) are based on very little data and will be refined as a consequence of the measurements made in this project.In a final work package, we will simulate and measure the kinetics of cloud droplet growth, specifically examining the condensation of organic compounds on a growing water droplet that can accompany the condensation of water. This has been highlighted very recently as a significant effect that has been largely ignored. Improved quantification of the condensation kinetics of organic compounds will allow the cloud droplet number to be better predicted, the sensitivity of which will be tested through cloud parcel models.In summary, this project will seek to reduce some of the uncertainties in quantifying the microphysical processes that occur on atmospheric aerosol particles and their impact on clouds.