A Novel Instrument for Characterising the Properties and Processes of Single Accumulation Mode Aerosol Particles

在模拟以前的气候变率和预测未来气候变化方面，气溶胶和云的影响仍然是最大的不确定因素之一。此外，已证明空气中的微粒对人类发病率和死亡率有重大影响，影响生活质量并影响大气能见度。更好地量化调节大气中颗粒特性的过程，对于提高我们对其影响的理解至关重要。通过大规模的野外活动，测量大气中颗粒的大小、组成和性质，可以获得大量关于气溶胶的信息。然而，在我们对大气气溶胶的理解变得更加完善之前，仍有一些关键的基本不确定性需要解决。特别是，我们对控制气溶胶性质的热力学、动力学和光学参数的理解仍存在相当大的不确定性。受控的实验室测量可以使我们以现场测量无法实现的方式直接解决其中一些关键的不确定性。应对这些挑战的传统实验室策略常常因为在对粒子群进行测量时固有的平均而变得复杂，由于无法描述定义系统的所有关键参数而受到损害，并且无法覆盖与大气中发现的气溶胶相关的时间尺度。该项目将寻求建立一个新的范例，用于研究控制大气气溶胶特性的热力学、动力学和光学参数。具体来说，一种新的光捕获技术将用于捕获和操纵单个亚微米颗粒，其尺寸范围与大气气溶胶特别相关，时间尺度不确定。这将与一种超灵敏技术相结合，以高时间分辨率探测捕获的气溶胶的大小和组成，从而开发出一种用于研究单个颗粒特性的新型原型仪器。新仪器将立即用于解决在理解气溶胶方面的三个关键不确定因素。首先，研究了气相吸附水对颗粒生长速率的动力学影响因素。这项研究将是有史以来第一次直接测量单个亚微米颗粒的大小变化动态。其次，将研究在过饱和条件下单个积累模式粒子的激活，允许对限制或促进云凝结核激活的因素进行详细调查，而不会因气溶胶样品组成和集合平均的不均匀性而产生歧义。最后，将研究单积累模式粒子的光学特性，为用于模拟大气中气溶胶光散射特性的建模方法提供严格的测试，它们对粒子大小和组成的依赖以及组分混合状态的影响。进行上述单一积聚模式粒子的研究将提供一种新颖而及时的方法来解决解释大气气溶胶的特性和过程中的一些挑战。

The influence of aerosols and clouds remains one of the largest uncertainties in modelling previous variabilities in climate and in predicting future climate change. In addition, airborne particulates have been shown to have a significant impact on human morbidity and mortality, influence quality of life and impact on atmospheric visibility. A better quantification of the processes that regulate the properties of particles in the atmosphere is central to improve our understanding of their impact. A considerable amount of information can be gained about aerosols by measuring the size, composition and properties of particles found in the atmosphere through large scale field campaigns. However, there remain a number of key fundamental uncertainties that need addressing before our understanding of atmospheric aerosol can become more fully refined. In particular, considerable uncertainty remains in our understanding of the thermodynamic, kinetic and optical parameters that govern aerosol properties. Controlled laboratory measurements can allow us to address some of these key uncertainties directly in a manner that is not possible from field measurements. Conventional laboratory strategies for tackling these challenges are frequently complicated by the inherent averaging that occurs when measurements are made on ensembles of particles, are compromised by an inability to characterise all of the key parameters defining the system, and are unable to cover the timescales relevant to aerosol found in the atmosphere. This project will seek to establish a new paradigm for investigating the thermodynamic, kinetic and optical parameters governing the properties of atmospheric aerosol. Specifically, a novel light trapping technique will be used to capture and manipulate single sub-micron particles, the size range particularly relevant to atmospheric aerosol, over indefinite timescales. This will be combined with an ultrasensitive technique for probing the size and composition of the captured aerosol with high time resolution, leading to the development of a novel prototype instrument for investigating the properties of single particles. The new instrument will immediately be used to address three of the key uncertainties in understanding aerosol. Firstly, the kinetic factors governing the growth rate of particles through the adsorption of water from the gas phase will be investigated. This study will be the first ever direct measurement of the size changing dynamics recorded on a single sub-micron particle. Secondly, the activation of a single accumulation mode particle under supersaturated conditions will be investigated, allowing a detailed investigation of the factors than limit or facilitate the activation of cloud condensation nuclei without the ambiguity that often arises from inhomogeneity in aerosol sample composition and ensemble averaging. Finally, the optical properties of single accumulation mode particles will be investigated, providing a rigorous test of the modelling approaches used to simulate the light scattering properties of aerosol in the atmosphere, their dependence on particle size and composition, and the influence of component mixing state. Performing the studies outlined above on single accumulation mode particles will provide a novel and timely approach to address some of the challenges in interpreting the properties and processes occurring on atmospheric aerosol.