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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Direct comparison of the hygroscopic properties of ammonium sulfate and sodium chloride aerosol at relative humidities approaching saturation
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Direct comparison of the hygroscopic properties of ammonium sulfate and sodium chloride aerosol at relative humidities approaching saturation

机译：直接比较硫酸铵和氯化钠气溶胶在相对湿度接近饱和时的吸湿性

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摘要

Holographic optical tweezers are used to make comparative measurements of the hygroscopic properties of single component aqueous aerosol containing sodium chloride and ammonium sulfate over a range of relative humidity from 84% to 96%. The change in RH over the course of the experiment is monitored precisely using a sodium chloride probe droplet with accuracy better than ±0.09%. The measurements are used to assess the accuracy of thermodynamic treatments of the relationship between water activity and solute mass fraction with particular attention focused on the dilute solute limit approaching saturation vapor pressure. The consistency of the frequently used Clegg-Brimblecombe-Wexler (CBW) treatment for predicting the hygroscopic properties of sodium chloride and ammonium sulfate aerosol is confirmed. Measurements of the equilibrium size of ammonium sulfate aerosol are found to agree with predictions to within an uncertainty of ±0.2%. Given the accuracy of treating equilibrium composition, the inconsistencies highlighted in recent calibration measurements of critical supersaturations of sodium chloride and ammonium sulfate aerosol cannot be attributed to uncertainties associated with the thermodynamic predictions and must have an alternative origin. It is concluded that the CBW treatment can allow the critical supersaturation to be estimated for sodium chloride and ammonium sulfate aerosol with an accuracy of better than ±0.002% in RH. This corresponds to an uncertainty of ≥1% in the critical supersaturation for typical supersaturations of 0.2% and above. This supports the view that these systems can be used to accurately calibrate instruments that measure cloud condensation nuclei concentrations at selected supersaturations. These measurements represent the first study in which the equilibrium properties of two particles of chemically distinct composition have been compared simultaneously and directly alongside each other in the same environment.
机译：全息光镊用于在相对湿度从84％到96％的范围内比较测量包含氯化钠和硫酸铵的单组分含水气溶胶的吸湿性能。在整个实验过程中，RH的变化可使用氯化钠探针滴进行精确监控，准确度优于±0.09％。这些测量值用于评估水活度和溶质质量分数之间关系的热力学处理的准确性，尤其要注意接近饱和蒸气压的稀溶质极限。证实了常用的Clegg-Brimblecombe-Wexler（CBW）处理用于预测氯化钠和硫酸铵气溶胶的吸湿性能的一致性。硫酸铵气溶胶平衡尺寸的测量结果与预测值相符，且不确定度在±0.2％内。鉴于处理平衡成分的准确性，近期对氯化钠和硫酸铵气雾剂的临界过饱和度的校准测量中突出显示的不一致之处，不能归因于与热力学预测有关的不确定性，而必须有其他来源。结论是，CBW处理可以估算出氯化钠和硫酸铵气溶胶的临界过饱和度，其相对湿度的准确度优于±0.002％。对于典型过饱和度为0.2％或更高的临界过饱和度，这对应于不确定性≥1％。这支持以下观点：这些系统可用于精确校准在选定过饱和度下测量云凝结核浓度的仪器。这些测量值代表了第一个研究，在该研究中，在同一环境中同时并彼此直接比较了化学成分不同的两个颗粒的平衡特性。

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