Diffusion and Equilibration in Viscous Atmospheric Aerosol

粘性大气气溶胶的扩散和平衡

• 批准号: NE/M004600/1
• 负责人: Jonathan Reid
• 金额: $ 37.36万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2014
• 资助国家: 英国
• 起止时间: 2014 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FM004600%2F1
• 关键词: Diffusion; Equilibration; Viscous; Atmospheric; Aerosol

Aerosols are a key component of the atmosphere. Defined as either solid particles or liquid droplets dispersed in the gas phase, aerosols can scatter and absorb sunlight and terrestrial infrared radiation influencing the radiation budget andhaving a direct effect on climate. They also act as nuclei on which water can condense, leading to the formation of cloud droplets, indirectly influencing the climate. As well as having many natural sources, they can form in polluted environments from the condensation of semi-volatile organic compounds forming secondary organic aerosol (SOA). The composition of SOA is rich in oxidised organic compounds and can contain organic molecules of high molecular weight. When the atmosphere is dry or cold, SOA particles can be highly viscous; indeed, it has been shown that SOA can exist as glassy particles. As such, droplets formed from water or formed from highly viscous SOA can differ in their viscosity by more than 15 orders of magnitude.Aerosol droplets that are largely water (eg. cloud droplets) have low viscosity, flow readily, and deform and spread when deposited. When exposed to changes in relative humidity and temperature, they can respond quickly to the change in the environment, losing or gaining water and also any semi-volatile or volatile organic compounds. They are, in essence, at equilibrium in composition with the surrounding gas phase. For particles approaching the glass transition, the particles do not deform and have the mechanical properties of a solid. They can only respond slowly to changes in the environment, losing or gaining water, semivolatile and volatile organic components only very slowly. Indeed, it can be estimated that such particles could in principle take many days to equilibrate and suggesting that SOA can exist in a kinetically arrested/hindered state in the atmosphere. Predicting the properties and impacts of aerosol in the atmosphere relies on knowing if the aerosol mass is in thermodynamic equilibrium or if it is kinetically limited, with significant consequences for understanding even the mass of aerosol in the atmosphere and the ability of the aerosol to form liquid cloud droplets or ice crystals.In this project, we will use a combination of single particle measurements, models and simulations to characterise the viscosity of ambient particles and the diffusion kinetics of water and organic components within viscous aerosol.Measurements will be made using individual particles captured in aerosol optical tweezers or in an electrodynamic balance. Light scattering measurements that allow the accurate determination of droplet size and refractive index will be used to examine the response of the particle to changes in environmental conditions. From the time-dependence of these changes, the diffusion of molecules within the particle can be determined. The viscosity can be measured directly by coalescing two particles and determining the timescale for the shape of the composite particle to relax to a sphere. Measurements of particles of simple and complex composition will be used to refine models of aerosol viscosity and molecular diffusion constants.In a final stage, the refined models will be used to assess the properties of viscous aerosol in the atmosphere. Initially, the role of viscous aerosol will be evaluated in a detailed model of the processes occurring in aerosol chamber measurements designed to simulate atmospheric aerosol. This will allow an assessment of the accuracy with which non-equilibrium kinetically limited aerosol processes can be captured and how sensitive the chamber measurements are to non-equilibrium effects. Finally, the sensitivity of atmospheric aerosol to non-equilibrium effects will be investigated using a wider scale regional model.In summary, we will seek to better define when aerosol can be considered to be at equilibrium and when kinetically limited in the atmosphere.

气溶胶是大气的重要组成部分。气溶胶被定义为分散在气相中的固体颗粒或液滴，可以散射和吸收阳光和地面红外辐射，从而影响辐射收支并对气候产生直接影响。它们还充当水可以凝结的核，导致云滴的形成，间接影响气候。它们不仅具有许多天然来源，还可以在污染环境中由半挥发性有机化合物冷凝形成二次有机气溶胶 (SOA) 形成。 SOA的成分富含氧化有机化合物，并且可以含有高分子量的有机分子。当大气干燥或寒冷时，SOA 颗粒可能会非常粘稠；事实上，已经证明 SOA 可以以玻璃状颗粒的形式存在。因此，由水形成的液滴或由高粘度 SOA 形成的液滴的粘度可能相差超过 15 个数量级。主要是水的气溶胶液滴（例如云滴）具有低粘度，易于流动，并且在沉积时变形和扩散。当暴露于相对湿度和温度的变化时，它们可以对环境的变化做出快速反应，失去或获得水分以及任何半挥发性或挥发性有机化合物。本质上，它们与周围气相的成分处于平衡状态。对于接近玻璃化转变的颗粒，颗粒不会变形并具有固体的机械性能。它们对环境变化的反应很慢，失去或获得水、半挥发性和挥发性有机成分的速度非常慢。事实上，可以估计，这些粒子原则上可能需要很多天才能达到平衡，这表明 SOA 可以在大气中以动力学停滞/受阻状态存在。预测大气中气溶胶的性质和影响依赖于了解气溶胶质量是否处于热力学平衡或是否受到动力学限制，这对于理解大气中气溶胶的质量以及气溶胶形成液云滴或冰晶的能力具有重要意义。在这个项目中，我们将结合使用单粒子测量、模型和模拟来表征环境粒子的粘度和 粘性气溶胶中水和有机成分的扩散动力学。将使用气溶胶光学镊子或电动天平捕获的单个颗粒进行测量。光散射测量可以准确确定液滴尺寸和折射率，用于检查颗粒对环境条件变化的响应。根据这些变化的时间依赖性，可以确定颗粒内分子的扩散。可以通过聚结两个颗粒并确定复合颗粒的形状松弛成球体的时间尺度来直接测量粘度。对简单和复杂成分的颗粒的测量将用于改进气溶胶粘度和分子扩散常数的模型。在最后阶段，改进的模型将用于评估大气中粘性气溶胶的特性。最初，将在旨在模拟大气气溶胶的气溶胶室测量中发生的过程的详细模型中评估粘性气溶胶的作用。这将允许评估捕获非平衡动力学限制气溶胶过程的准确性以及室测量对非平衡效应的敏感度。最后，将使用更广泛的区域模型来研究大气气溶胶对非平衡效应的敏感性。总之，我们将寻求更好地定义气溶胶何时可以被认为处于平衡状态以及何时在大气中受到动力学限制。

项目成果

Viscosity of erythritol and erythritol-water particles as a function of water activity: new results and an intercomparison of techniques for measuring the viscosity of particles

赤藓糖醇和赤藓糖醇-水颗粒的粘度作为水活度的函数：新结果和颗粒粘度测量技术的相互比较

• DOI: 10.5194/amt-2018-136
• 发表时间: 2018
• 作者: Chu Y

Identifying time-dependent changes in the morphology of an individual aerosol particle from its light scattering pattern

• DOI: 10.1080/02786826.2019.1661351
• 发表时间: 2019-09-14
• 期刊: AEROSOL SCIENCE AND TECHNOLOGY
• 影响因子: 5.2
• 作者: Haddrell, Allen;Rovelli, Grazia;Reid, Jonathan
• 通讯作者: Reid, Jonathan

Viscous organic aerosol particles in the upper troposphere: diffusivity-controlled water uptake and ice nucleation?

• DOI: 10.5194/acp-15-13599-2015
• 发表时间: 2015-01-01
• 期刊: ATMOSPHERIC CHEMISTRY AND PHYSICS
• 影响因子: 6.3
• 作者: Lienhard, D. M.;Huisman, A. J.;Peter, T.
• 通讯作者: Peter, T.

Predictions of diffusion rates of organic molecules in secondary organic aerosols using the Stokes-Einstein and fractional Stokes-Einstein relations

使用斯托克斯-爱因斯坦和分数斯托克斯-爱因斯坦关系预测二次有机气溶胶中有机分子的扩散速率

• DOI: 10.5194/acp-2019-191
• 发表时间: 2019
• 作者: Evoy E

Predictions of diffusion rates of large organic molecules in secondary organic aerosols using the Stokes-Einstein and fractional Stokes-Einstein relations

• DOI: 10.5194/acp-19-10073-2019
• 发表时间: 2019-08-09
• 期刊: ATMOSPHERIC CHEMISTRY AND PHYSICS
• 影响因子: 6.3
• 作者: Eyoy, Erin;Maclean, Adrian M.;Bertram, Allan K.
• 通讯作者: Bertram, Allan K.