McGrory Megan R, Shepherd Rosalie H, King Martin D, Davidson Nicholas, Pope Francis D, Watson I Matthew, Grainger Roy G, Jones Anthony C, Ward Andrew D
Central Laser Facility, Research Complex, STFC Rutherford Appleton Laboratory, Oxford, OX11 0FA, UK.
Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, UK.
Phys Chem Chem Phys. 2022 Mar 9;24(10):5813-5822. doi: 10.1039/d1cp04068e.
Sulfuric acid is shown to form a core-shell particle on a micron-sized, optically-trapped spherical silica bead. The refractive indices of the silica and sulfuric acid, along with the shell thickness and bead radius were determined by reproducing Mie scattered optical white light as a function of wavelength in Mie spectroscopy. Micron-sized silica aerosols (silica beads were used as a proxy for atmospheric silica minerals) were levitated in a mist of sulfuric acid particles; continuous collection of Mie spectra throughout the collision of sulfuric acid aerosols with the optically trapped silica aerosol demonstrated that the resulting aerosol particle had a core-shell morphology. Contrastingly, the collision of aqueous sulfuric acid aerosols with optically trapped polystyrene aerosol resulted in a partially coated system. The light scattering from the optically levitated aerosols was successfully modelled to determine the diameter of the core aerosol (±0.003 μm), the shell thickness (±0.0003 μm) and the refractive index (±0.007). The experiment demonstrated that the presence of a thin film rapidly changed the light scattering of the original aerosol. When a 1.964 μm diameter silica aerosol was covered with a film of sulfuric acid 0.287 μm thick, the wavelength dependent Mie peak positions resembled sulfuric acid. Thus mineral aerosol advected into the stratosphere would likely be coated with sulfuric acid, with a core-shell morphology, and its light scattering properties would be effectively indistinguishable from a homogenous sulfuric acid aerosol if the film thickness was greater than a few 100 s of nm for UV-visible wavelengths.
结果表明，硫酸在微米级、光阱捕获的球形二氧化硅珠上形成了核壳颗粒。在米氏光谱中，通过重现作为波长函数的米氏散射光学白光，测定了二氧化硅和硫酸的折射率，以及壳层厚度和珠半径。微米级二氧化硅气溶胶（用二氧化硅珠作为大气二氧化硅矿物的替代物）悬浮在硫酸颗粒的雾中；在硫酸气溶胶与光阱捕获的二氧化硅气溶胶碰撞的整个过程中持续收集米氏光谱，结果表明生成的气溶胶颗粒具有核壳形态。相比之下，硫酸水气溶胶与光阱捕获的聚苯乙烯气溶胶碰撞产生了部分包覆的体系。成功模拟了光悬浮气溶胶的光散射，以确定核心气溶胶的直径（±0.003μm）、壳层厚度（±0.0003μm）和折射率（±0.007）。实验表明，薄膜的存在迅速改变了原始气溶胶的光散射。当直径为1.964μm的二氧化硅气溶胶被0.287μm厚的硫酸膜覆盖时，与波长相关的米氏峰位置类似于硫酸。因此，平流层中被输送的矿物气溶胶可能会被硫酸包覆，形成核壳形态，并且如果膜厚度对于紫外-可见光波长大于几百纳米，其光散射特性将与均匀的硫酸气溶胶有效区分不开。
