Water Vapor Depletion in the DMT Continuous-Flow CCN Chamber: Effects on Supersaturation and Droplet Growth
Water Vapor Depletion in the DMT Continuous-Flow CCN Chamber: Effects on Supersaturation and Droplet Growth
复制标题
DOI：
10.1080/02786826.2010.551146
复制
发表时间：
2011-02
影响因子：
5.2
通讯作者：
T. Lathem;A. Nenes
中科院分区：
文献类型：
--
作者：
T. Lathem;A. Nenes
连续流流动热梯度云凝结核计数器(CFSTGC)是一种商用仪器，广泛用于云凝结核(CCN)的实验室和野外测量。到目前为止，所有的研究都假设在其生长室中产生的过饱和度分布不受水蒸气对生长中的CCN的冷凝的影响。然而，这一假设的有效性从未被系统地探讨过。这项工作考察了CCN的水蒸气消耗何时会对过饱和度、测量的CCN浓度和液滴生长产生重要影响。采用全耦合数值模型模拟了CFSTGC内的水蒸气过饱和度、温度、速度分布以及在大范围运行和CCN浓度范围内的CCN生长。用多分散定标气溶胶的实验室CCN活化实验(DMT CFSTGC在恒流模式下运行)对模拟结果进行了评估。然后，通过对导致过饱和耗尽的条件进行比例分析，对模拟和实验室实验进行了概括。我们发现，低于5000 cm−3的CCN浓度(无论其活化动力学或仪器操作条件)不会使过饱和度和出口液滴直径减少超过10%。对于较大的CCN浓度，可以应用简单的校正，同时解决过饱和度和液滴大小的降低问题。
The continuous-flow streamwise thermal-gradient cloud condensation nuclei counter (CFSTGC) is a commercially available instrument that is widely used for laboratory and field measurements of cloud condensation nuclei (CCN). All studies to date assume that the supersaturation profile generated in its growth chamber is not influenced by the condensation of water vapor upon the growing CCN. The validity of this assumption, however, has never been systematically explored. This work examines when water vapor depletion from CCN can have an important impact on supersaturation, measured CCN concentration, and droplet growth. A fully coupled numerical flow model of the instrument is used to simulate the water vapor supersaturation, temperature, velocity profiles, and CCN growth in the CFSTGC for a wide range of operation and CCN concentrations. Laboratory CCN activation experiments of polydisperse calibration aerosol (with a DMT CFSTGC operated in constant flow mode) are used to evaluate the simulations. The simulations and laboratory experiments are then generalized using a scaling analysis of the conditions that lead to supersaturation depletion. We find that CCN concentrations below 5000 cm−3 (regardless of their activation kinetics or instrument operating conditions) do not decrease supersaturation and outlet droplet diameter by more than 10%. For larger CCN concentrations, a simple correction can be applied that addresses both the depression in supersaturation and droplet size.