The Impacts of Phase Separation and Particle Shape on Aerosol Optical Properties Measured using Single Particle Cavity Ring-Down Spectroscopy

大气气溶胶粒子调节着地球的气候，但对它们的描述是气候模型中最大的不确定性之一。特别是，光与不同形状和内部结构的大气粒子的相互作用知之甚少。形态复杂的气溶胶的光学特性对于理解疾病传播也很重要。例如，在人类呼气过程中发出的含有病原体的液滴被认为表现出多个阶段，1，2和理解它们的光学特性是设计可以改善公共健康的消毒设备的核心。液滴采用球形，其光学性质的计算是直接的。然而，固体颗粒（例如通过干燥含有溶解盐的水滴形成的颗粒）采用各种形状，以复杂的方式散射和吸收光。颗粒还采用各种各样的内部结构。例如，由有机和无机物质的混合物组成的含水颗粒可能经历液-液相分离（LLPS），其光学性质将不同于均匀颗粒的预期光学性质，很少有研究测量形状或LLPS对气溶胶光学性质的影响，其精度或灵敏度足以挑战描述形态复杂颗粒的光学模型。

Atmospheric aerosol particles regulate Earth's climate, yet their description represents one of the largest uncertainties in climate models. In particular, the interactions of light with atmospheric particles of varying shape and internal structure are understood poorly. The optical properties of morphologically complex aerosols are also important in understanding disease transmission. For example, pathogen-containing droplets emitted during human exhalation are thought to exhibit multiple phases,1,2 and understanding their optical properties is central to designing sterilisation devices that could improve public health. Liquid droplets adopt spherical shapes for which the calculation of optical properties are straightforward. However,solid particles (such as those formed through drying of aqueous droplets that contain dissolved salts) adopt a wide range of shapes that scatter and absorb light in complex ways. Particles also adopt a wide range of internal structures. For example, an aqueous particle comprised of a mixture of organic and inorganic species may undergo liquid-liquid phase separation (LLPS), the optical properties for which will differ from those expected of a homogeneous particle.Few studies have measured the impacts of shape or LLPS on aerosol optical properties with sufficient accuracy or sensitivity to challenge optical models thatdescribe morphologically complex particles.