MRI: Development of a Cylindrical Cloud Condensation Nuclei (CCN) Spectrometer

这是一项重大研究仪器奖，旨在设计和建造一种用于测量云凝结核（CCN）活动谱的新仪器。 其工作原理是，空气缓慢而连续地通过一个热梯度扩散室，其中过饱和度随着进入该室的距离的增加而增加。 在腔室的出口处，已经形成的云滴被光学颗粒计数器计数并确定大小。 然后，使用数学反演程序从测量的液滴光谱计算CCN光谱，假设液滴的大小和其形成的临界过饱和度之间的关系。 拟议的仪器是对现有设计的改进，有两个原因：现代数字电子设备将用于粒子检测和计数，以及通过使用同心圆柱形壁，云室将呈环形，而不是简单的矩形通道。 环形形状的优点是消除了与侧壁相关的不期望的边缘效应。 该仪器提供的信息是云微物理学的基础，也关系到在数值气候模式中处理气溶胶粒子及其辐射效应的方式。

This is a Major Research Instrumentation award to enable the design and construction of a new instrument for measuring the activity spectrum of cloud condensation nuclei (CCN). The principle of operation is that air is drawn slowly and continuously through a thermal-gradient diffusion chamber in which the supersaturation increases with increasing distance into the chamber. At the exit of the chamber, the cloud droplets that have formed are counted and sized with an optical particle counter. A mathematical inversion procedure is then used to compute the CCN spectrum from the measured droplet spectrum, assuming a relationship between the size of a droplet and the critical supersaturation at which it formed. The proposed instrument is an improvement over existing designs for two reasons: modern digital electronics will be used for particle detection and counting, and by use of concentric cylindrical walls the cloud chamber will be in the shape of an annulus instead of a simple rectangular channel. The advantage of the annular shape is that undesirable edge effects associated with side walls are eliminated. The information provided by the instrument is fundamental for cloud microphysics and also bears on the way aerosol particles and their radiative effects are treated in numerical climate models.