CAREER: Effects of Chemical Aging on the Ice Nucleation Properties of Natural and Anthropogenic Atmospheric Particles

通过这项由美国国家科学基金会化学部环境化学科学项目资助的职业奖项，卡内基梅隆大学的瑞安·沙利文教授正在实验研究大气化学处理对环境中颗粒引发(成核)的冰形成的影响。虽然已知化学反应会改变冰核粒子的冻结特性，但目前对云层和气候模型中水滴变成冰粒子的过程的描述主要基于新鲜(或未老化)粒子的特性。通过确定现实粒子系统冻结特性的变化，这项研究提高了我们对人类活动如何影响云演化和冰形成的理解。开发将借给K-12教师的教育模块，使年轻学生接触到化学科学以及空气污染、酸雨和云形成反应的测量。CMU本科生仪器分析核心课程开设了一系列新的动手实验室实验，增强了大学生在现代化学分析方面的培训。矿物粉尘和火山灰颗粒，以及生物质燃烧(木烟)气溶胶，使用室内或流动管反应器进行化学老化，以确定人为污染物对大气处理对这些重要的自然成冰颗粒来源的接触和浸泡冻结特性的影响。化学老化对颗粒组成、混合状态和冰核特性的影响是通过在线和离线单颗粒表征的广泛组合来确定的。这包括使用两个单粒子质谱仪进行在线分析，以及对颗粒和冰晶残留物进行离线光谱分析。这些颗粒系统的接触冻结效率是使用冷却气溶胶光学镊子系统直接测量的。利用油冷板系统中的液滴，获得了液滴中颗粒的浸没冻结温度谱。这项研究产生了一个全面的数据集，关于重要类型的冰核粒子的非均相成冰特性，以及大气处理对其冻结能力的影响。这些测量被参数化，以改进云和大气化学模式中生物质燃烧和矿物颗粒的化学成分和相关的冰核特性的表示。

Through this CAREER award funded by the Environmental Chemical Sciences Program in the Chemistry Division at the National Science Foundation, Professor Ryan Sullivan of Carnegie Mellon University is experimentally investigating the effects of atmospheric chemical processing on ice formation initiated (nucleated) by particles in the environment. While chemical reactions are known to alter the freezing properties of ice-nucleating particles, current representations of the process by which water droplets become ice particles in cloud and climate models are largely based on the properties of fresh (or unaged) particles. By determining the changes in the freezing properties of realistic particle systems, this research advances our understanding of how human activities affect cloud evolution and ice formation. The development of educational modules to be loaned to K-12 teachers expose young students to the chemical science and measurement of air pollution, acid rain, and cloud forming reactions. The creation of a series of new hands-on laboratory experiments for the core undergraduate instrumental analysis course at CMU enhances the training of college students in modern chemical analysis.Mineral dust and volcanic ash particles, and biomass burning (wood smoke) aerosol, is chemically aged using a chamber or flow tube reactor to determine the effects of atmospheric processing by anthropogenic pollutants on the contact and immersion freezing properties of these important natural sources of ice-nucleating particles. The effects of chemical aging on particle composition, mixing state, and ice nucleation properties are determined using an extensive combination of online and offline single-particle characterization. This includes online analysis using two single-particle mass spectrometers, and offline spectromicroscopic analysis of particles and ice crystal residues. The contact freezing efficiency of these particle systems is directly measured using a chilled aerosol optical tweezers system. Immersion freezing temperature spectra of particles immersed in droplets is obtained using a droplet in oil cold plate system. This research produces a comprehensive dataset regarding the heterogeneous ice nucleation properties of important types of ice nucleating particles, and the effects of atmospheric processing on their freezing ability. The measurements is parameterized to produce improved representations of the chemical composition and related ice nucleation properties of biomass burning and mineral particles in cloud and atmospheric chemistry models.