CAREER: Size Resolved Measurement of Cloud Condensation Nuclei Concentration and Properties

这笔赠款支持设计和制造一种新的仪器，用于研究作为云滴形成凝结核的大气气溶胶。该仪器由差示迁移率分析仪(DMA)和云凝结核分离器(CCNS)组成，前者将气溶胶颗粒分成不同大小的颗粒，后者将吸湿性较强的颗粒与吸湿性较弱的颗粒分开。可以作为凝聚核的是吸湿粒子。CCNS由两个同心圆柱体组成，两个圆柱体之间施加一个电场。圆柱体之间的环形区域基本上是一个热梯度扩散腔。通过湿滤纸将内、外壁保持在不同的温度和水饱和度，从而使它们之间的空间过饱和。当粒子离开DMA时，它们被带电，施加在CCNS上的电场使它们随着空气通过腔室而缓慢地向内壁迁移。粒子的电迁移率随着凝聚的增长而降低。因此，变大的粒子比保持较小的粒子迁移到内壁的机会更少。从最初进入CCNS的大小接近的颗粒中，吸湿性较小的颗粒沉积在内壁上，而那些在施加过饱和时充当CCN的颗粒通过。因此，两级仪器使研究不同尺寸范围内气溶胶粒子的成核特性成为可能。作为分析的进一步步骤，可以使用单粒子质谱仪来确定离开仪器的CCN的化学成分。这项研究的结果与云形成的基本物理和气溶胶对云的太阳反射率的影响有关。这个职业奖的教育部分包括为本科生开设的关于气象和大气化学测量的技术、应用和实用方面的暑期课程。该课程的高潮是在加利福尼亚州马里纳进行的为期一周的现场活动，以利用跨学科遥控飞机研究中心(CIRPAS)的研究设施进行空中观测为中心。

This grant supports the design and fabrication of a novel instrument for studying the atmospheric aerosols that serve as condensation nuclei for the formation of cloud droplets. The instrument consists of a differential mobility analyzer (DMA), which separates the aerosol particles into a narrow range of sizes, followed by a cloud condensation nucleus separator (CCNS), which separates the more hygroscopic particles from the less hygroscopic ones. It is the hygroscopic particles that can serve as condensation nuclei. The CCNS consists of two concentric cylinders, between which an electric field is applied. The annular region between the cylinders is basically a thermal gradient diffusion chamber. The inner and outer walls are maintained at different temperatures and at water saturation by means of wet filter paper, so that the space between them is supersaturated. The particles are charged when they leave the DMA, and the field applied to the CCNS causes them to migrate slowly towards the inner wall as they move with the air through the chamber. The electrical mobility of the particles is reduced as they grow by condensation. Hence the particles that grow large have less chance of migrating to the inner wall than those that remain small. From the initial population of near-equal sized particles that enter the CCNS, the less hygroscopic ones are thus deposited on the inner wall, and those that serve as CCN at the applied supersaturation pass through. The two-stage instrument therefore makes it possible to study the nucleating properties of aerosol particles in different size ranges. As a further step in the analysis, the chemical composition of the CCN that exit the instrument may be determined using a single-particle mass spectrometer. Results of the research are relevant to the basic physics of cloud formation and to the question of aerosol effects on the solar reflectivity of clouds.The educational component of this CAREER award consists of a summer course for undergraduate students on techniques, applications, and practical aspects of meteorological and atmospheric chemical measurements. The culmination of the course is a week-long field campaign in Marina, CA, centered on airborne observations with the research facilities of the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS).