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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >A New Optical Technique to Study Aerosol Phase Transitions: The Nucleation of Ice from H_2SO_4 Aerosols
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A New Optical Technique to Study Aerosol Phase Transitions: The Nucleation of Ice from H_2SO_4 Aerosols

机译：研究气溶胶相变的新光学技术：H_2SO_4气溶胶中冰的核化

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摘要

A new optical microscope technique has been developed to investigate phase transitions in micrometer-sized droplets. This technique has been used to study the nucleation of ice from aqueous H_2SO_4 aerosols 0-35 wt % in composition in the temperature range from 273 to 170 K. The aerosols were produced with a nebulizer and were deposited on a quartz plate, which was coated with a hydrophobic silane monolayer to minimize the effects of heterogeneous nucleation. More than 1200 aerosol particles were monitored individually with the optical microscope, and their freezing temperatures and melting points were recorded. The observed freezing temperatures are lower than the ones from comparable aerosol studies reported in the literature, the differences in the freezing temperature being up to 30 K, especially for the more concentrated aerosols. No freezing was observed above 170 K for compositions greater than 27 wt %. A thermodynamic model has been used to apply the new freezing temperature data to the formation of clouds in the upper troposphere and lower stratosphere. The results indicate that the homogeneous nucleation of ice particles in cirrus clouds requires saturation ratios with respect to ice ranging from about 1.5 at 230 K to 1.6 at 205 K. In addition, the formation of type II polar stratospheric clouds under volcanically perturbed conditions where H_2SO_4 is the main aqueous aerosol component at low temperatures is predicted to occur about 3 K below the ice frost point.
机译：已经开发出一种新的光学显微镜技术来研究微米级液滴中的相变。这项技术已被用于研究0-35 wt％的H_2SO_4水性气溶胶在273至170 K温度范围内冰的成核作用。该气溶胶由雾化器生产，并沉积在石英板上，然后进行涂覆疏水性硅烷单层膜可以最大程度地减少异质成核的影响。用光学显微镜分别监测了1200多个气溶胶颗粒，并记录了它们的凝固温度和熔点。观测到的冰点温度低于文献报道的可比气雾剂研究的冰点温度，其中冰点温度的差异高达30 K，尤其是对于浓度更高的气雾剂。对于大于27wt％的组合物，在170K以上未观察到冻结。一个热力学模型已被用于将新的冻结温度数据应用于对流层上部和平流层下部的云团的形成。结果表明，卷云中冰粒的均匀成核需要相对于冰的饱和比范围从230 K时的1.5到205 K时的1.6。此外，在H_2SO_4受到火山扰动的条件下，II型极地平流层云的形成是低温下主要的水气溶胶成分，预计会在冰霜点以下约3 K处发生。

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