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

卡内基梅隆大学的Ryan Sullivan教授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CAREER奖，正在实验研究大气化学过程对由环境中粒子引发（成核）的冰形成的影响。虽然已知化学反应会改变冰核颗粒的冻结特性，但目前在云和气候模型中，水滴变成冰粒的过程主要是基于新鲜（或未老化）颗粒的特性。通过确定现实粒子系统冻结特性的变化，本研究促进了我们对人类活动如何影响云演化和冰形成的理解。教育模块的开发将借给K-12教师，让年轻学生了解化学科学以及空气污染、酸雨和云形成反应的测量。在CMU的核心本科仪器分析课程中，创建了一系列新的动手实验，加强了大学生对现代化学分析的训练。矿物粉尘和火山灰颗粒，以及生物质燃烧（木烟）气溶胶，使用室或流管反应器进行化学老化，以确定人为污染物的大气处理对这些重要的冰核颗粒自然来源的接触和浸泡冻结特性的影响。化学老化对颗粒组成、混合状态和冰核性质的影响是通过在线和离线单颗粒表征的广泛结合来确定的。这包括使用两台单粒子质谱仪进行在线分析，以及对粒子和冰晶残留物进行离线光谱显微镜分析。使用冷冻气溶胶光学镊子系统直接测量了这些粒子系统的接触冻结效率。以油冷板系统中的液滴为实验对象，获得了颗粒在液滴中的浸没冻结温度谱。本研究建立了重要冰核颗粒非均质冰核性质的综合数据集，以及大气处理对其冻结能力的影响。在云和大气化学模型中，测量结果被参数化，以产生生物质燃烧和矿物颗粒的化学成分和相关冰核特性的改进表示。

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.