Reducing the Uncertainties in Aerosol Hygroscopic Growth

气溶胶和云是地球大气的重要组成部分，影响辐射收支和化学成分，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往气候观测和预测未来气候变化方面最大的不确定因素之一。气溶胶和云可以散射和吸收阳光和地面辐射，通过改变入射太阳辐射和流出红外光的平衡，对气候产生直接影响。气溶胶对气候有间接影响，影响云层的反照率和寿命。所有的云滴都是由更小的气溶胶粒子种子形成的，水可以在这些粒子种子上凝结。地球大气中气溶胶颗粒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）具有更强的吸湿性，因此对水具有不同的亲和力，从而改变了云滴形成的条件。气溶胶对气候的这种间接影响受到的限制很少，通常会抵消大气中温室气体含量增加所引起的变暖，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及其作为云凝结核的能力的因素。我们会模拟气溶胶过程在单粒子被光或电场,测量他们的发展规模与高时间分辨率(比10 ms)和高精度(比+ / - 0.5%)。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颗粒大小随相对湿度的变化，其准确度比以前可能的要高得多，甚至达到云滴形成的条件。这些新数据记录的气溶胶颗粒含有广泛的有机和无机溶质，这些溶质是大气中发现的典型成分，这些新数据将为气溶胶颗粒在云滴中的生长建模提供更大的限制。在第二个工作包中，我们将研究控制平衡和随时间变化的云滴表面组成的因素。不同于体积的表面成分，是决定气溶胶颗粒变成云滴有多容易的关键因素。目前的表面成分（张力）模型是基于非常少的数据，并将在这个项目中进行测量的结果进行改进。在最后一个工作包,我们将模拟和测量云滴增长的动力学,专门研究有机化合物的缩合越来越水滴,可以伴随水的凝结。这是最近被强调的一个很大程度上被忽视的重大影响。有机化合物凝结动力学的改进量化将使云滴数得到更好的预测，其灵敏度将通过云包模型进行测试。总而言之，本项目将设法减少对大气气溶胶粒子及其对云的影响的微物理过程进行量化的一些不确定性。

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.