Studies of heterogeneous freezing by three different desert dust samples
Studies of heterogeneous freezing by three different desert dust samples
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DOI：
10.5194/acp-9-2805-2009
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发表时间：
2009-01-01
影响因子：
6.3
通讯作者：
Gallagher, M.
中科院分区：
文献类型：
--
作者：
Connolly, P. J.;Moehler, O.;Gallagher, M.
我们展示了大气气溶胶相互作用和动力学 (AIDA) 室设施的实验结果，研究了三种不同类型的矿物颗粒在 -12 摄氏度到 -33 摄氏度之间的温度下水的冻结。这三种不同的粉尘是亚洲粉尘 1 (AD1)、撒哈拉粉尘 2 (SD2) 和亚利桑那试验粉尘 (ATD)。使用的灰尘样品的颗粒浓度大小呈对数正态分布，众数直径在 0.3 至 0.5 μm 之间，标准偏差 sigma(g) 为 1.6-1.9。冷冻实验的结果与冰成核的奇异假设一致。尘埃表现出不同的成核能力，ATD 在低于 -24 摄氏度的温度下表现出冰活性表面位点密度的急剧增加。AD1 是第二个最有效的冷冻核，并且比 ATD 样品表现出更逐渐的活性增加。 SD2 是最不活跃的冷冻核。我们使用粒子计数探针获取的数据来推导灰尘上形成的冰活性表面位点密度，作为三个样品中每一个的温度的函数，并将多项式曲线拟合到该数据。然后在箱微物理模型中独立使用曲线拟合来模拟实验中的冰形成速率，以测试用平滑曲线参数化数据的有效性。 AD1 和 SD2 的测量结果与模型之间具有良好的一致性；然而，ATD 曲线并没有产生与观察结果非常吻合的结果。其原因是需要在 -20 至 -24 摄氏度之间进行更多实验来量化在此温度范围内 ATD 上冰活性表面位点密度的急剧增加。所呈现的曲线可用作大气云模型中的参数化，其中存在约 1 ℃ min(-1) 或更高的冷却速率，以预测通过冰成核的冷凝-冻结模式形成的冰晶的浓度。最后，对所有三个样本进行多项式拟合，以便进行参数化，描述三个灰尘样本的等量混合物的平均冰活性表面位点密度与温度的关系。
We present results of experiments at the aerosol interactions and dynamics in the atmosphere (AIDA) chamber facility looking at the freezing of water by three different types of mineral particles at temperatures between -12 degrees C and -33 degrees C. The three different dusts are Asia Dust-1 (AD1), Sahara Dust-2 (SD2) and Arizona test Dust (ATD). The dust samples used had particle concentrations of sizes that were log-normally distributed with mode diameters between 0.3 and 0.5 mu m and standard deviations, sigma(g), of 1.6-1.9. The results from the freezing experiments are consistent with the singular hypothesis of ice nucleation. The dusts showed different nucleation abilities, with ATD showing a rather sharp increase in ice-active surface site density at temperatures less than -24 degrees C. AD1 was the next most efficient freezing nuclei and showed a more gradual increase in activity than the ATD sample. SD2 was the least active freezing nuclei. We used data taken with particle counting probes to derive the ice-active surface site density forming on the dust as a function of temperature for each of the three samples and polynomial curves are fitted to this data. The curve fits are then used independently within a bin microphysical model to simulate the ice formation rates from the experiments in order to test the validity of parameterising the data with smooth curves. Good agreement is found between the measurements and the model for AD1 and SD2; however, the curve for ATD does not yield results that agree well with the observations. The reason for this is that more experiments between -20 and -24 degrees C are needed to quantify the rather sharp increase in ice-active surface site density on ATD in this temperature regime. The curves presented can be used as parameterisations in atmospheric cloud models where cooling rates of approximately 1 degrees C min(-1) or more are present to predict the concentration of ice crystals forming by the condensation-freezing mode of ice nucleation. Finally a polynomial is fitted to all three samples together in order to have a parameterisation describing the average ice-active surface site density vs. temperature for an equal mixture of the three dust samples.