Cleaning up our water: reducing interferences from nonhomogeneous freezing of "pure" water in droplet freezing assays of ice-nucleating particles
Cleaning up our water: reducing interferences from nonhomogeneous freezing of "pure" water in droplet freezing assays of ice-nucleating particles
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DOI：
10.5194/amt-11-5315-2018
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发表时间：
2018-09-24
影响因子：
3.8
通讯作者：
Sullivan, Ryan C.
中科院分区：
文献类型：
--
作者：
Polen, Michael;Brubaker, Thomas;Sullivan, Ryan C.
半个世纪以来，液滴冻结技术 (DFT) 一直用于测量大气中冰核颗粒 (INP) 的浓度，并确定其冻结特性，以了解 INP 对混合相云的影响。冰成核界最近采用液滴冷冻测定作为常见的实验方法。这些液滴冷冻实验通常受到污染的限制，污染导致用于在所测量的异质冷冻温度范围内生成液滴的“纯”水不均匀冷冻。水早期结冰的干扰常常被忽视并且没有得到充分报告，或者测量仅限于分析冰活性更强的 INP，这些 INP 的结冰温度远高于背景水的温度。然而，这种避免对于分析大气中活性较低的 INP 的冻结行为是不可行的，因为 INP 仍然对冷云微物理具有潜在的重要影响。在这项工作中，我们回顾了一些最近的液滴冷冻技术，这些技术在减少这些干扰方面显示出巨大的前景，并且我们报告了我们自己使用类似方法进行的广泛系列测量。通过表征放置液滴的不同基材和不同纯水生成技术的性能，我们推荐减少这些干扰的最佳实践。我们测试了不同的基质、水源、液滴矩阵和液滴尺寸，以更深入地了解最适合 DFT 的方法。还提出了分析液滴冻结温度光谱以及对背景“纯”水控制光谱进行计算和校正的方法。最后，我们提出了未来均质和异质冰成核研究的实验和数据分析程序，以促进更统一和可靠的方法，促进通过 DFT 测量的冰成核颗粒的相互比较。
Droplet freezing techniques (DFTs) have been used for half a century to measure the concentration of ice-nucleating particles (INPs) in the atmosphere and determine their freezing properties to understand the effects of INPs on mixed-phase clouds. The ice nucleation community has recently adopted droplet freezing assays as a commonplace experimental approach. These droplet freezing experiments are often limited by contamination that causes nonhomogeneous freezing of the "pure" water used to generate the droplets in the heterogeneous freezing temperature regime that is being measured. Interference from the early freezing of water is often overlooked and not fully reported, or measurements are restricted to analyzing the more ice-active INPs that freeze well above the temperature of the background water. However, this avoidance is not viable for analyzing the freezing behavior of less active INPs in the atmosphere that still have potentially important effects on cold-cloud microphysics. In this work we review a number of recent droplet freezing techniques that show great promise in reducing these interferences, and we report our own extensive series of measurements using similar methodologies. By characterizing the performance of different substrates on which the droplets are placed and of different pure water generation techniques, we recommend best practices to reduce these interferences. We tested different substrates, water sources, droplet matrixes, and droplet sizes to provide deeper insight into what methodologies are best suited for DFTs. Approaches for analyzing droplet freezing temperature spectra and accounting and correcting for the background "pure" water control spectrum are also presented. Finally, we propose experimental and data analysis procedures for future homogeneous and heterogeneous ice nucleation studies to promote a more uniform and reliable methodology that facilitates the ready intercomparison of ice-nucleating particles measured by DFTs.