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

大气中的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，人们对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性质对理解疾病传播也很重要。例如，在人体呼气过程中释放的含有病原体的飞沫被认为具有多相1,2，了解它们的光学特性对于设计可以改善公众健康的灭菌装置至关重要。液滴采用球形，其光学性质的计算很简单。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）采用多种形状，以复杂的方式散射和吸收光。粒子也采用多种内部结构。例如，由有机和无机物质的混合物组成的水粒子可能经历液-液相分离（LLPS），其光学性质将不同于预期的均匀粒子。很少有研究以足够的精度或灵敏度测量形状或LLPS对气溶胶光学特性的影响，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.